ADVANCED RADIO TELECOM CORP
SC 13D, 1999-09-20
RADIOTELEPHONE COMMUNICATIONS
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                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                   ----------

                                  SCHEDULE 13D
                                 (RULE 13D-101)

             INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT
            TO RULE 13D-1(a) AND AMENDMENTS THERETO FILED PURSUANT TO
                                  RULE 13D-2(a)


                          ADVANCED RADIO TELECOM CORP.
                          ----------------------------
                                (Name of Issuer)

                          COMMON STOCK, $.001 PAR VALUE
                          -----------------------------
                         (Title of Class of Securities)

                                   0075-4U-101
                                   -----------
                                 (CUSIP Number)

                  (Name, Address and Telephone Number of Person
                Authorized to Receive Notices and Communications)

                                SEPTEMBER 8, 1999
                                -----------------
                      (Date of Event Which Requires Filing
                               of This Statement)

         If the filing person has previously filed a statement on Schedule 13G
to report the acquisition that is the subject of this Schedule 13D, and is
filing this schedule because of Rule 13d-1(e), 13d-1(f) or 13d-1(g), check the
following box [  ].

               NOTE. Schedules filed in paper format shall include a signed
          original and five copies of the schedule, including all exhibits. SEE
          Rule 13d-7(b) for other parties to whom copies are to be sent.

                         (Continued on following pages)
                              (Page 1 of 229 Pages)
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 2 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Oak Investment Partners VIII, Limited Partnership
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      3,493,470
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    PN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW

<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 3 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Oak VIII Affiliate Fund, Limited Partnership
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      67,660
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    PN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW

<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 4 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    MeriTech Capital Partners L.P.
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      2,190,090
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    PN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 5 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    MeriTech Capital Affiliates L.P.
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      35,610
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    PN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 6 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Accel VI L.P.
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      1,087,030
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    PN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 7 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Accel Internet Fund II L.P.
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      138,880
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    PN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 8 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Accel Keiretsu VI L.P.
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      17,360
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    PN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 9 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Accel Investors '98 L.P.
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      92,140
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    PN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 10 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Brentwood Associates IX, L.P.
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      1,295,360
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    PN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 11 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Brentwood Affiliates Fund III, L.P.
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      40,060
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    PN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 12 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Worldview Technology Partners II, L.P.
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      990,250
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    PN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 13 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Worldview Technology International II, L.P.
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      303,140
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    PN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 14 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Worldview Strategic Partners II, L.P.
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      42,040
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    PN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 15 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Bessemer Venture Partners IV L.P.
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      267,080
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    PN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 16 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Bessec Ventures IV L.P.
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      178,060
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    PN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 17 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Cove Ventures, LLC
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      267,080
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    OO
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 18 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Adams Capital Management, L.P.
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      267,080
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    PN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 19 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Columbia ARTT Investors, LLC
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Virginia
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      890,280
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    OO
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 20 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Columbia ARTT Partners, LLC
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Virginia
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      890,280
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    OO
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 21 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Global Private Equity II-Europe Limited Partnership
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      89,030
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    PN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 22 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Global Private Equity II-PGGM Limited Partnership
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      222,570
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    PN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 23 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Digital Media and Communications II Limited Partnership
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      192,300
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    PN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW

<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 24 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Oakstone Ventures Limited Partnership
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      137,380
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    PN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 25 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Advent Crown Fund II C.V.
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Netherlands
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      137,380
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    PN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 26 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Adwest Limited Partnership
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      35,610
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    PN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 27 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Advent Global GECC Limited Partnership
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      890,280
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    PN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 28 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Advent Partners Limited Partnership
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    OO
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    61,524(1)
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      137,554(2)
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,407,594*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.1%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    PN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW

- -------------
(1) Represents shares of Common Stock previously acquired, none of which are
    subject to the Purchase Agreement, Stockholders Agreement or Standstill
    Agreement (each as defined below).
(2) Includes shares described in previous footnote.
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 29 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Advent International Limited Partnership
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS

- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    1,258,780(3)
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      2,963,330(4)
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    23,604,850*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    47.5%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    PN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW

- -------------
(3) Represents shares of Common Stock beneficially owned by Global Private
    Equity II Limited Partnership (see Item 5 of the text below), none of which
    are subject to the Purchase Agreement, Stockholders Agreement or Standstill
    Agreement (each as defined below).
(4) Includes shares described in previous footnote.

<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 30 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Advent International Corporation
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS

- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    1,321,511(5)
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      3,100,884(6)
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    23,667,581*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    47.7%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    CO, IA
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW

- -------------

(5) Represents 1,258,780 shares of Common Stock beneficially owned by Global
    Private Equity II Limited Partnership, 61,524 shares of common stock held by
    Advent Partners Limited Partnership and 1,207 shares of common stock owned
    by Advent International Investors II Limited Partnership (see Item 5 of the
    text below), none of which are subject to the Purchase Agreement,
    Stockholders Agreement or Standstill Agreement (each as defined below).
(6) Includes shares described in previous footnote.

<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 31 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Advent Global Management Limited Partnership
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS

- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      890,280
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    PN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW

<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 32 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Qwest Communications Corporation
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS

- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      8,012,540
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    CO
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>

- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 33 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Qwest Corporation
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS

- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Colorado
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      8,012,540
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    CO
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 34 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Qwest Communications International Inc.
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS

- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      8,012,540
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    CO
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 35 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Anschutz Company
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS

- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      8,012,540
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    CO
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 36 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    Philip F. Anschutz
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS

- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    U.S.
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      8,012,540
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    IN
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
- --------------------------                              ------------------------
CUSIP NO. 0075-4U-101                 13D               Page 37 of 229
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
1   NAME OF REPORTING PERSON
    I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
    U.S. Telesource, Inc.
- --------------------------------------------------------------------------------
2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                    (a) [X]
                                                                         (b) [ ]
- --------------------------------------------------------------------------------
3   SEC USE ONLY
- --------------------------------------------------------------------------------
4   SOURCE OF FUNDS
    AF
- --------------------------------------------------------------------------------
5   CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
    TO ITEM 2(d) OR 2(e)                                                     [ ]
- --------------------------------------------------------------------------------
6   CITIZENSHIP OR PLACE OF ORGANIZATION
    Delaware
- --------------------------------------------------------------------------------
          NUMBER OF            7      SOLE VOTING POWER
            SHARES                    0
         BENEFICIALLY          -------------------------------------------------
           OWNED BY            8      SHARED VOTING POWER
             EACH                     22,346,070*
       REPORTING PERSON        -------------------------------------------------
             WITH              9      SOLE DISPOSITIVE POWER
                                      8,012,540
                               -------------------------------------------------
                               10     SHARED DISPOSITIVE POWER
                                      0
- --------------------------------------------------------------------------------
11  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
    22,346,070*
- --------------------------------------------------------------------------------
12  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES    [ ]
- --------------------------------------------------------------------------------
13  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
    45.0%
- --------------------------------------------------------------------------------
14  TYPE OF REPORTING PERSON
    CO
- --------------------------------------------------------------------------------
                            *SEE ITEM 4 OF TEXT BELOW
<PAGE>
                                                                  Page 38 of 229

ITEM 1.  SECURITY AND ISSUER

         This statement relates to the Common Stock, $.001 par value ("Common
Stock") of Advanced Radio Telecom Corp., a Delaware corporation (the "Company"),
which has its principal executive offices at 500 108th Avenue NE, Suite 2600,
Bellevue, Washington 98004.

ITEM 2.  IDENTITY AND BACKGROUND

         This statement is filed by Oak Investment Partners VIII, Limited
Partnership ("OIP"), Oak VIII Affiliate Fund, Limited Partnership ("OAF") (OIP
and OAF together being hereinafter referred to as "Oak"), MeriTech Capital
Partners L.P. ("Cap"), MeriTech Capital Affiliates L.P. ("Affiliates") (Cap and
Affiliates together being hereinafter referred to as "MeriTech"), Accel VI L.P.
("Accel VI"), Accel Internet Fund II L.P. ("Accel Internet"), Accel Keiretsu VI
L.P. ("Accel Keiretsu"), Accel Investors '98 L.P. ("Accel Investors"), Brentwood
Associates IX, L.P. ("Brentwood IX"), Brentwood Affiliates Fund III, L.P.
("Brentwood III"), Worldview Technology Partners II, L.P. ("WTP"), Worldview
Technology International II, L.P. ("WTI"), Worldview Strategic Partners II, L.P.
("WSP") (WTP, WTI and WSP collectively being hereinafter referred to as
"Worldview"), Bessemer Venture Partners IV L.P. ("Bessemer"), Bessec Ventures IV
L.P. ("Bessec"), Cove Ventures LLC ("CoveVentures"), Adams Capital Management,
L.P. ("Adams Capital"), Columbia ARTT Investors, LLC ("Columbia Investors"),
Columbia ARTT Partners, LLC ("Columbia Partners") (Columbia Investors and
Columbia Partners together being hereinafter referred to as "Columbia"), Global
Private Equity II-Europe Limited Partnership ("GPEII Europe"), Global Private
Equity II-PGGM Limited Partnership ("GPEIIPGGM"), Digital Media & Communications
II Limited Partnership ("Digital"), Oakstone Ventures Limited Partnership
("Oakstone"), Advent Crown Fund II C.V. ("Advent Crown"), Adwest Limited
Partnership ("Adwest"), Advent Global GECC Limited Partnership ("Advent
Global"), Advent Partners Limited Partnership ("Advent Partners"), Advent
International Limited Partnership ("Advent International"), Advent International
Corporation ("Advent Corporation"), Advent Global Management Limited Partnership
("Advent Partnership") (Advent Crown, Adwest, GPEII-Europe, GPEIIPGGM, Digital,
Advent Global, Oakstone, Advent Partners, Advent International, Advent
Corporation and Advent Partnership collectively being hereinafter referred to as
"Advent"), U.S. Telesource, Inc. ("USTI"), Qwest Corporation ("QC"), Qwest
Communications Corporation ("QCC"), Qwest Communications International Inc.
("QCI"), Anschutz Company ("AC") and Philip F. Anschutz ("Anschutz"), all of
whom collectively are sometimes hereinafter referred to as the "Reporting
Persons."

         OIP is a Delaware limited partnership with its principal and business
address at 525 University Avenue, Suite 1300, Palo Alto, California 94301. The
principal business of OIP is venture capital investment.

         OAF is a Delaware limited partnership with its principal and business
address at 525 University Avenue, Suite 1300, Palo Alto, California 94301. The
principal business of OAF is venture capital investment.

<PAGE>
                                                                  Page 39 of 229

         Cap is a Delaware limited partnership with its principal and business
address at 428 University Avenue, Palo Alto, California 94301. The principal
business of Cap is venture capital investment.

         Affiliates is a Delaware limited partnership with its principal and
business address at 428 University Avenue, Palo Alto, California 94301. The
principal business of Affiliates is venture capital investment.

         Accel VI is a Delaware limited partnership with its principal and
business address at 428 University Avenue, Palo Alto, California 94301. The
principal business of Accel VI is venture capital investment.

         Accel Internet is a Delaware limited partnership with its principal and
business address at 428 University Avenue, Palo Alto, California 94301. The
principal business of Accel Internet is venture capital investment.

         Accel Keiretsu is a Delaware limited partnership with its principal and
business address at 428 University Avenue, Palo Alto, California 94301. The
principal business of Accel Keiretsu is venture capital investment.

         Accel Investors is a Delaware limited partnership with its principal
and business address at 428 University Avenue, Palo Alto, California 94301. The
principal business of Accel Investors is venture capital investment.

         Brentwood IX is a Delaware limited partnership with its principal and
business address at 3000 Sand Hill Road, Building 1, Suite 260, Menlo Park,
California 94025. The principal business of Brentwood IX is venture capital
investment.

         Brentwood III is a Delaware limited partnership with its principal and
business address at 3000 Sand Hill Road, Building 1, Suite 260, Menlo Park,
California 94025. The principal business of Brentwood III is venture capital
investment.

         WTP is a Delaware limited partnership with its principal and business
address at 435 Tasso, Suite 120, Palo Alto, California 94301. The principal
business of WTP is venture capital investment.

         WTI is a Delaware limited partnership with its principal and business
address at 435 Tasso, Suite 120, Palo Alto, California 94301. The principal
business of WTI is venture capital investment.

         WSP is a Delaware limited partnership with its principal and business
address at 435 Tasso, Suite 120, Palo Alto, California 94301. The principal
business of WSP is venture capital investment.
<PAGE>
                                                                  Page 40 of 229

         Bessemer is a Delaware limited partnership with its principal and
business address at 1400 Old Country Road, Suite 407, Westbury, New York 11590.
The principal business of Bessemer is venture capital investment.

         Bessec is a Delaware limited partnership with its principal and
business address at 1400 Old Country Road, Suite 407, Westbury, NY 11590. The
principal business of Bessec is venture capital investment.

         CoveVentures is a limited liability company formed under the laws of
the State of Delaware with its principal and business address at 1013 Cove Road,
Mamaroneck, New York 10543. The principal business of CoveVentures is venture
capital investment.

         Adams Capital is a Pennsylvania limited partnership with its principal
and business address at 518 Broad Street, Sewickley, Pennsylvania 15143. The
principal business of Adams Capital is venture capital investment.

         Columbia Investors is a limited liability company formed under the laws
of the State of Virginia with its principal and business address at 201 North
Union Street, Suite 300, Alexandria, Virginia 22314. The principal business of
Columbia Investors is venture capital investment.

         Columbia Partners is a limited liability company formed under the laws
of the State of Virginia with its principal and business address at 201 North
Union Street, Suite 300, Alexandria, Virginia 22314. The principal business of
Columbia Partners is venture capital investment.

         GPEII-Europe is a Delaware limited partnership with its principal and
business address at 75 State Street, Boston, Massachusetts 02109. The principal
business of GPEII-Europe is private equity investment.

         GPEIIPGGM is a Delaware limited partnership with its principal and
business address at 75 State Street, Boston, Massachusetts 02109. The principal
business of GPEIIPGGM is private equity investment.

         Digital is a Delaware limited partnership with its principal and
business address at 75 State Street, Boston, Massachusetts 02109. The principal
business of Digital is private equity investment.

         Advent Corporation is a Delaware corporation with its principal and
business address at 75 State Street, Boston, Massachusetts 02109. Advent
Corporation is an investment advisory firm. Advent Corporation is the General
Partner of Advent Partners and Advent International, which is in turn the
general partner of GPEII Europe, Digital, Oakstone, Advent Crown, Adwest,
GPEIIPGGM, and Advent Partnership, which is in turn the general partner of
Advent Global. The principal business of Advent Corporation is private equity
investments.

         Advent International is a Delaware limited partnership with its
principal and business address at 75 State Street, Boston, Massachusetts 02109.
Advent International is the general partner of GPEII Europe, Digital, Oakstone,
Advent Crown, Adwest, GPEIIPGGM and Advent
<PAGE>
                                                                  Page 41 of 229

Partnership, which is in turn the general partner of Advent Global. The
principal business of Advent International is private equity investments.

         Advent Partnership is a Delaware limited partnership with its principal
and business address at 75 State Street, Boston, Massachusetts 02109. Advent
Partnership is the general partner of Advent Global. The principal business of
Advent Partnership is private equity investments.

         Oakstone is a Delaware limited partnership with its principal and
business address at 75 State Street, Boston, Massachusetts 02109. The principal
business of Oakstone is private equity investment.

         Advent Crown is a Netherlands limited partnership with its principal
and business address at 75 State Street, Boston, Massachusetts 02109. The
principal business of Advent Crown is private equity investment.

         Adwest is a Delaware limited partnership with its principal and
business address at 75 State Street, Boston, Massachusetts 02109. The principal
business of Adwest is private equity investments.

         Advent Global is a Delaware limited partnership with its principal and
business address at 75 State Street, Boston, Massachusetts 02109. The principal
business of Advent Global is private equity investments.

         Advent Partners is a Delaware limited partnership with its principal
and business address at 75 State Street, Boston, Massachusetts 02109. The
principal business of Advent Partners is private equity investments.

         USTI is a Delaware corporation and a direct wholly owned subsidiary of
QCC. QC is a Colorado Corporation and a direct fully owned subsidiary of QCI.
QCC is a Delaware corporation and a direct wholly owned subsidiary of QC. QCI is
a publicly-traded Delaware corporation. AC is the beneficial owner of
approximately 39% of the outstanding shares of QCI. Anschutz is the beneficial
owner of 100% of the capital stock of AC. USTI's, QCC's, QCI's, AC's and
Anschutz's principal and business address is 555 17th Street, Denver, Colorado
80202. The principal business of USTI is to acquire and hold securities and
other investment assets. The principal business of QCC and QCI is providing
voice, image and data communications. The principal business of AC and Anschutz
is railroad transportation, communications, natural resources, real estate and
sports entertainment.

         The Reporting Persons may constitute a "group" for purposes of
Regulation 13D-G promulgated under the Securities Exchange Act of 1934.

         The name, state or other place of organization, principal business,
address of principal business and address of principal office of each of the
persons enumerated in Instruction C with respect to the Reporting Persons
(collectively, the "Control Parties") that is a corporation, general
partnership, limited partnership, syndicate or other group of persons is as set
forth in Exhibit B hereto, and the name, residence or business address, present
principal occupation or employment,
<PAGE>
                                                                  Page 42 of 229

the name, principal business and address of any corporation or other
organization in which such employment is conducted and the citizenship of each
of the Control Parties that is a natural person is as set forth on Exhibit B.

         None of the Reporting Persons or the Control Parties has been, during
the last five years, (a) convicted in a criminal proceeding (excluding traffic
violations or similar misdemeanors), or (b) party to a civil proceeding of a
judicial or administrative body of competent jurisdiction and as a result of
such proceeding was or is subject to a judgment, decree or final order enjoining
future violations of, or prohibiting or mandating activities subject to federal
or state securities laws or finding any violation with respect to such laws.

ITEM 3.  SOURCE AND AMOUNT OF FUNDS OR OTHER CONSIDERATION

         The aggregate amount of funds used in making the purchase of the Series
A Shares (as defined in Item 4 below) is $251 million. USTI obtained its portion
of such funds from one of its affiliates. Each of the other Reporting Persons
that purchased Series A Shares obtained its portion of such funds from other
sources.

ITEM 4.  PURPOSE OF TRANSACTION

         On September 9, 1999, the Reporting Persons other than Advent
International, Advent Corporation, Advent Partnership, QCC, QC, QCI, AC and
Anschutz (such Reporting Persons being collectively referred to herein as the
"Purchasers") purchased, in the aggregate, 2,234,607 shares of the Company's
Series A Convertible Preferred Stock (the "Series A Shares") pursuant to that
certain Preferred Stock Purchase Agreement dated as of June 1, 1999 (the
"Purchase Agreement") by and among the Company and the Purchasers, a copy of
which is attached hereto as Exhibit C. Each Series A Share is convertible into
10 shares of Common Stock at any time at the option of the holder thereof. The
number of shares of Common Stock beneficially owned by each of the Reporting
Persons by virtue of their beneficial ownership of Series A Shares, on an
as-converted basis, is indicated in the table of beneficial ownership of Common
Stock set forth in Item 5(a). Each Purchaser also acquired shares of Series B
Non-Voting Preferred Stock of the Company (the "Series B Shares") (the Series A
Shares and Series B Shares being collectively hereinafter referred to as the
"Shares"). Advent Corporation, Advent International and Advent Partners, who
acquired beneficial ownership of 1,780,580 shares of Common Stock, 1,704,550
shares of Common Stock and 76,030 shares of Common Stock, respectively, pursuant
to their acquisition of Series A Shares pursuant to the Purchase Agreement,
separately also hold 1,321,511 shares of Common Stock, 1,258,780 shares of
Common Stock and 61,524 shares of Common Stock, respectively. This statement
relates to the acquisition of beneficial ownership of the Common Stock into
which the Series A Shares may be converted and beneficial ownership of the
Common Stock held separately by Advent Corporation, Advent International and
Advent Partners.

         Pursuant to the terms of the Purchase Agreement, the Company has agreed
to take all necessary action to cause a nominee of USTI and a nominee of Oak to
be added to the Board of Directors of the Company. So long as USTI has not sold
or transferred more than three-quarters of the number of Shares purchased by
USTI under the Purchase Agreement or three-quarters of
<PAGE>
                                                                  Page 43 of 229

the common shares of the Company into which the Shares are convertible, USTI
will retain the right to nominate one director for each regular election of the
Company's board of directors. So long as the Purchasers (other than Columbia,
Advent and USTI) have not sold or transferred more than three-quarters of the
number of Shares purchased by the Purchasers (other than Columbia, Advent and
USTI) under the Purchase Agreement or three-quarters of the common shares of the
Company into which the Shares are convertible, Oak will retain the right to
nominate one person for director at each regular election of the Company's board
of directors.

         In connection with the Purchase Agreement, the Purchasers entered into
a Stockholders Agreement dated as of June 1, 1999 (the "Stockholders
Agreement"), attached hereto as Exhibit D. Pursuant to the Stockholders
Agreement, each Purchaser agreed to vote its Series A Shares to elect the
nominee of USTI and the nominee of Oak to the Board of Directors of the Company.
Furthermore, each Purchaser other than Columbia and Advent agreed to vote its
Series A Shares as to all other matters as Oak and USTI jointly direct. However,
the Stockholders Agreement provides that if Oak and USTI are unable to agree as
to how to vote on any matter, each Purchaser is free to vote its Series A Shares
in its discretion. The Stockholders Agreement further provides that if USTI
transfers to any person other than any of its affiliates more than 50% of the
number of Shares acquired by Oak, MeriTech and Worldview under the Purchase
Agreement, each Purchaser other than Columbia and Advent shall vote its Series A
Shares as Oak directs, and that if Oak, MeriTech or Worldview, individually or
in the aggregate, transfer to any person other than any of their respective
affiliates more than 50% of the number of Shares acquired by USTI under the
Purchase Agreement, each Purchaser other than Columbia and Advent shall vote its
Series A Shares as USTI directs.

         The Stockholders Agreement also sets forth certain restrictions on the
ability of the Purchasers to transfer their Series A Shares. Up until such time
as the Series A Shares are automatically converted into common stock of the
Company (which automatic conversion will occur (a) upon a public offering of the
Company yielding at least $75,000,000 in proceeds at a price per share of
$18.00, (b) on the first date after June 2001 on which the closing price of the
Company's common stock has exceeded $18.00 per share for at least 30 of 40
consecutive trading days, (c) upon the approval of the holders of two-thirds of
the Series A Shares or (d) upon the conversion into common stock of the Company
or Series C Junior Preferred Stock of the Company of seventy-five percent of the
Shares), none of the Purchasers may transfer their Series A Shares except to
their affiliates or by way of distribution to their limited partners, and except
for transfers registered pursuant to and in compliance with the Registration
Rights Agreement (described in Item 6 below). Each Purchaser that is a limited
partnership also agreed not to transfer any Series A Shares to its limited
partners prior to the date on which directors are elected at the Company's 2000
annual meeting of stockholders.

         The Purchasers other than Columbia and Advent and the Company also
entered into a Standstill Agreement dated as of June 1, 1999 (the "Standstill
Agreement"), attached hereto as Exhibit E. The Standstill Agreement will remain
in effect until the earlier of (i) the fourth anniversary after the Purchasers
have acquired the Shares under the Purchase Agreement and (ii) the date as of
which neither Oak nor USTI is entitled to nominate a director to the Company's
Board of Directors in accordance with the Purchase Agreement.
<PAGE>
                                                                  Page 44 of 229

         During the term of the Standstill Agreement, the Purchasers that are
party thereto may not (i) acquire equity securities or material assets of the
Company except (a) pursuant to a stock split, stock dividend, recapitalization
or reclassification, (b) upon the conversion of the Series A Shares into common
stock of the Company, (c) pursuant to the Rights Agreement dated as of June 20,
1997 between the Company and Bank Boston, N.A. or (d) pursuant to the "Special
Stock Purchase Rights" granted in the Purchase Agreement, (ii) participate in
any proxy solicitation, (iii) form, be a member of or join any group for the
purpose of voting the Company's securities or acquiring the Company's securities
or assets other than the group formed pursuant to the Stockholders Agreement,
(iv) deposit any voting stock of the Company into a voting trust or subject any
voting stock of the Company to any arrangement or agreement with respect to the
voting of the Series A Shares other than the Stockholders Agreement, (v) seek to
place on the Board or remove from the Board, directors other than the USTI or
Oak nominees, (vi) call or seek to call a meeting of the Stockholders of the
Company other than as a director or the Company, (vii) solicit, negotiate, or
provide information with respect to a merger or sale of all or a substantial
portion of the assets of the Company, except for Purchasers discussing proposals
of third parties with the Company or (viii) instigate, encourage or assist, or
enter into any discussions or arrangements with any third party to do or take
any of the actions described above.

         The Standstill Agreement also contains certain restrictions on transfer
of the Series A Shares. Until the second anniversary after the Purchasers have
acquired the Shares under the Purchase Agreement, no Purchaser that is party to
the Standstill Agreement may transfer any Series A Shares other than (i) to
affiliates that agree to be bound by the Standstill Agreement, (ii) by way of
distribution to its limited partners or former limited partners which are not
affiliates of such Purchaser, (iii) in a private transfer to a person who is not
an affiliate of such Purchaser and that would own less than ten percent of the
total voting power of the Company, and (iii) pursuant to a public sale under
Rule 144 of the Securities Act of 1933 or pursuant to the exercise of rights
under the Registration Rights Agreement (described in Item 6 below).

         The standstill and transfer restrictions set forth in the Standstill
Agreement are subject to temporary suspension in the event of (i) the
commencement of a tender offer for fifty percent of the outstanding shares of
voting securities of the Company, but only if the Company has not, within ten
days of such commencement, publicly recommended the tender offer not be
accepted, or if all of the material conditions to such offer relating to the
elimination or satisfaction of the material defensive provisions established by
the Company have been satisfied or waived, (ii) the Company's receipt of an
acquisition proposal (as defined in the Standstill Agreement) and if the Company
has not rejected the acquisition proposal within fifteen days, (iii) a Change of
Control (as defined in the Standstill Agreement), (iv) a public announcement by
the Company that it is "for sale," (v) the execution of a definitive agreement
by the Company that would result in a Change of Control (as defined in the
Standstill Agreement), (vi) the announcement, which is not publicly opposed by
the Company's Board of Directors within ten days of the announcement, of the
commencement of a proxy contest that would result in a majority of the directors
of the Company being elected or removed, or (vii) the adoption of a plan of
liquidation of the Company.

         The purpose of the acquisition of the Series A Shares by the Reporting
Persons is to make an equity investment in the Company. In addition, in
connection therewith, QCC and the
<PAGE>
                                                                  Page 45 of 229

Company have entered into certain commercial arrangements pursuant to which the
Company agreed to purchase certain services from QCC, co-locate equipment with
QCC where desirable and jointly market its products with QCC where desirable.

         USTI and its affiliates have considered and continue to explore certain
other strategic and/or commercial relationships with the Company, some of which
may include actions of the type described in items (a) through (j) of Item 4 of
Schedule 13D.

         While the Reporting Persons that are party to the Standstill Agreement
have no present intention to take any actions that are prohibited by the
standstill and transfer restrictions set forth in the Standstill Agreement, such
Reporting Persons may take one or more of such actions in the event that such
restrictions are suspended under the circumstances described above or upon
termination of the Standstill Agreement, whether by its terms or otherwise.

         The summaries of the terms of the Purchase Agreement, the Standstill
Agreement and the Stockholders Agreement set forth herein are not intended to be
complete and are qualified in their entirety by reference to the full text of
such agreements, copies of which are filed as Exhibits hereto.

ITEM 5.  INTEREST IN SECURITIES OF THE ISSUER

         (a)      AGGREGATE AMOUNT BENEFICIALLY OWNED AND PERCENT OF CLASS:

                  The number of shares of Common Stock beneficially owned by
                  each Reporting Person upon conversion of the Series A Shares
                  beneficially owned by such Reporting Person, and the number of
                  shares of Common Stock owned of record by each Reporting
                  Person, is set forth in the table below:

<PAGE>
                                                                  Page 46 of 229
<TABLE>
<CAPTION>
                            NUMBER OF SHARES OF
                                COMMON STOCK                                     NUMBER OF SHARES OF
                          BENEFICIALLY OWNED WITH     NUMBER OF SHARES OF           COMMON STOCK
                            RESPECT TO SERIES A      COMMON STOCK OWNED OF          BENEFICIALLY
REPORTING PERSON                   SHARES                    RECORD*                    OWNED
- ----------------          -----------------------    ---------------------       -------------------
<S>                                <C>                                                <C>
OIP                                3,493,470                                          22,346,070
OAF                                   67,660                                          22,346,070
Cap                                2,190,090                                          22,346,070
Affiliates                            35,610                                          22,346,070
Accel VI                           1,087,030                                          22,346,070
Accel Internet                       138,880                                          22,346,070
Accel Keiretsu                        77,360                                          22,346,070
Accel Investors                       92,140                                          22,346,070
Brentwood IX                       1,295,360                                          22,346,070
Brentwood III                         40,060                                          22,346,070
WTP                                  990,250                                          22,346,070
WTI                                  303,140                                          22,346,070
WSP                                   42,040                                          22,346,070
Bessemer                             267,080                                          22,346,070
Bessec                               178,060                                          22,346,070
Cove Ventures                        267,080                                          22,346,070
Adams Capital                        267,080                                          22,346,070
Columbia Investors                   890,280                                          22,346,070
Columbia Partners                    890,280                                          22,346,070
GPEII Europe                          89,030                                          22,346,070
GPEIIPGGM                            222,570                                          22,346,070
Digital                              192,300                                          22,346,070
Oakstone                             137,380                                          22,346,070
Advent Crown                         137,380                                          22,346,070
Adwest                                35,610                                          22,346,070
Advent Global                        890,280                                          22,346,070
Advent Partners                       76,030                    61,524*               22,407,594
Advent Corporation (1)             1,780,580                 1,321,511*               23,667,581
Advent International (2)           1,704,550                 1,258,780*               23,604,580
Advent Partnership (3)               890,280                                          22,346,070
USTI                               8,012,540                                          22,346,050
QCC                                8,012,540                                          22,346,050
QC                                 8,012,540                                          22,346,070
QCI                                8,012,540                                          22,346,050
AC                                 8,012,540                                          22,346,050
Anschutz                           8,012,540                                          22,346,070
</TABLE>

- --------------------
*    Common Stock not subject to the Purchase Agreement, Stockholders Agreement
     or the Standstill Agreement.
(1)  Advent Corporation is the general partner of Advent Partners and Advent
     International, which is in turn the general partner of GPEII Europe,
     Digital, Oakstone, Advent Crown, Adwest, GPEIIPGGM, Global Private Equity
     II Limited Partnership, Advent International Investors II Limited
     Partnership and Advent Partnership, which is in turn the General Partner of
     Advent Global. As such, Advent Corporation has the power to vote and
     dispose of the securities owned by the entities in the previous sentence.
     The beneficial ownership of Advent Corporation derives from such power.
(2)  Advent International is the general partner of GPEII Europe, Digital,
     Oakstone, Advent Crown, Adwest, Global Private Equity II Limited
     Partnership, Advent International Investors II Limited Partnership,
     GPEIIPGGM and Advent Partnership, which is in turn the general partner of
     Advent Global. As such, Advent International has the power to vote and
     dispose of the securities owned by the aforementioned entities. The
     beneficial ownership of Advent International derives from such power.
(3)  Advent Partnership is the General Partner of Advent Global. As such, Advent
     Partnership has the power to vote and dispose of the securities owned by
     Advent Global. The beneficial ownership of Advent Partnership derives from
     such power.
<PAGE>
                                                                  Page 47 of 229

Because the Reporting Persons may constitute a "group" for purposes of
Regulation 13D-G promulgated under the Securities Exchange Act of 1934 with
respect to the Series A Shares beneficially owned by them, each Reporting Person
is the beneficial owner of 22,346,070 shares of Common Stock issuable upon
conversion of the Series A Shares, representing 45.0% of the outstanding Common
Shares.

Advent Corporation, Advent International and Advent Partners beneficially own an
additional 1,321,511, 1,258,780 and 61,524 shares of Common Stock, respectively,
not subject to the Purchase Agreement, Stockholders Agreement or the Standstill
Agreement, resulting in beneficial ownership of 47.7%, 47.5% and 45.1% of the
outstanding Common Stock (including the Series A Shares on an as converted
basis).

         NUMBER OF SHARES OF COMMON STOCK AS TO WHICH REPORTING PERSONS LISTED
         IN TABLE IN ITEM 5(a) ABOVE (OTHER THAN ADVENT INTERNATIONAL, ADVENT
         CORPORATION AND ADVENT PARTNERS) HOLD:


         (i)      Sole power to vote or to direct the vote:  0
         (ii)     Shared power to vote or to direct the vote: 22,346,070 (See
                  Item 4 above)
         (iii)    Sole power to dispose or to direct the disposition: See Number
                  of Shares of Common Stock Beneficially Owned With Respect to
                  Series A Shares set forth in table in Item 5(a) above
         (iv)     Shared power to dispose or to direct the disposition:  0

         NUMBER OF SHARES OF COMMON STOCK AS TO WHICH ADVENT INTERNATIONAL
         HOLDS:

         (i)      Sole power to vote or to direct the vote:  1,258,780
         (ii)     Shared power to vote or to direct the vote: 22,346,070 (See
                  Item 4 above)
         (iii)    Sole power to dispose or to direct the disposition:  2,963,330
         (iv)     Shared power to dispose or to direct the disposition:  0

         NUMBER OF SHARES OF COMMON STOCK AS TO WHICH ADVENT CORPORATION HOLDS:

         (i)      Sole power to vote or to direct the vote:  1,321,511
         (ii)     Shared power to vote or to direct the vote: 22,346,070 (See
                  Item 4 above)
         (iii)    Sole power to dispose or to direct the disposition:  3,100,884
         (iv)     Shared power to dispose or to direct the disposition:  0

         NUMBER OF SHARES OF COMMON STOCK AS TO WHICH ADVENT PARTNERS HOLDS:

         (i)      Sole power to vote or to direct the vote:  61,524
         (ii)     Shared power to vote or to direct the vote: 22,346,070 (See
                  Item 4 above)
         (iii)    Sole power to dispose or to direct the disposition:  137,554
         (iv)     Shared power to dispose or to direct the disposition:  0
<PAGE>

                                                                  Page 48 of 229

         TRANSACTIONS IN THE PREVIOUS 60 DAYS:

         To the extent that an acquisition of Series A Shares constitutes a
         transaction in Common Stock, the Reporting Persons effected a
         transaction in Common Stock when they acquired beneficial ownership of
         Common Stock by virtue of their acquisition of Series A Shares at the
         closing of the transactions contemplated by the Purchase Agreement on
         September 9, 1999. 2,234,607 Series A Shares were purchased directly
         from the issuer in a private transaction for an aggregate consideration
         of $251 million.

         ANY OTHER PERSON KNOWN TO HAVE THE RIGHT TO RECEIVE OR THE POWER TO
         DIRECT DIVIDENDS

         Not applicable.

         DATE ON WHICH THE REPORTING PERSON CEASED TO BE A BENEFICIAL OWNER OF
         MORE THAN FIVE PERCENT OF THE CLASS OF SECURITIES:

         Not applicable.

ITEM 6.  CONTRACTS, ARRANGEMENTS, UNDERSTANDINGS OR RELATIONSHIPS WITH RESPECT
         TO SECURITIES OF THE ISSUER

         See Item 4 for a description of the Purchase Agreement, the Standstill
Agreement and the Stockholders Agreement, which description is incorporated
herein by this reference.

         Each Series A Share may be converted into ten shares of the Company's
common stock at any time at the option of the holder thereof. Each of the
Purchasers and the Company have also entered into a Registration Rights
Agreement dated as of June 1, 1999 (the "Registration Rights Agreement")
pursuant to which the Purchasers are entitled to certain demand registration
rights and incidental registration rights with respect to shares of the common
stock of the Company into which the Shares are converted (the "Registrable
Shares").

         Purchasers holding in the aggregate in excess of 50% of the Registrable
Shares may demand, no more than twice in any twelve-month period, that the
Company register the Registrable Shares on six occasions, so long as the market
value of the shares registered at any one time is at least $25 million. The
Purchasers also may demand that the Company register the Registrable Shares on
Form S-3 an unlimited number of times, so long as the market value of the shares
registered at any one time is at least $20 million.

         If, at any time prior to June 1, 2004, the Company proposes to register
any of its shares other than on Form S-4 or Form S-8, the Company, at the
request of any Purchaser, must use its best efforts to include the common stock
issuable on conversion of the Series A Shares in such registration.
<PAGE>
                                                                  Page 49 of 229

ITEM 7.  MATERIAL TO BE FILED AS EXHIBITS

EXHIBIT A:  Joint Filing Statement.

EXHIBIT B:  Name, residence or business address, present principal occupation or
            employment and name, principal business and address of any
            corporation or other organization in which such employment is
            conducted of each of the Control Parties that is a natural person.

EXHIBIT C:  Preferred Stock Purchase Agreement

EXHIBIT D:  Stockholders Agreement

EXHIBIT E:  Standstill Agreement
<PAGE>
                                                                  Page 50 of 229

                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                               September 16, 1999



                               Oak Investment Partners VIII, Limited Partnership
                               By: Oak Associates VIII, LLC
                               Its General Partner

                               /s/ BANDEL CARANO
                               -------------------------------------------------
                               By: Bandel Carano
                               Title: General Partner
<PAGE>
                                                                  Page 51 of 229


                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                   September 16, 1999



                                   Oak VIII Affiliate Fund, Limited Partnership
                                   By: Oak VIII Affiliates, LLC
                                   Its General Partner

                                   /s/ BANDEL CARANO
                                   ---------------------------------------------
                                   By: Bandel Carano
                                   Title: General Partner

<PAGE>
                                                                  Page 52 of 229


                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                         September 16, 1999


                                         MeriTech Capital Partners, L.P.


                                         By: MeriTech Capital Associates LLC
                                                Its General Partner

                                         By: MeriTech Management Associates LLC
                                                A managing member


                                         By: /s/ PAUL MADERA
                                            -----------------------------------
                                                 Paul Madera, a managing member

<PAGE>
                                                                  Page 53 of 229


                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                      September 16, 1999


                                      MeriTech Capital Affiliates L.P.


                                      By: MeriTech Capital Associates L.L.C.
                                             Its General Partner

                                      By: MeriTech Management Associates L.L.C.
                                             A managing member


                                      By: /s/ PAUL MADERA
                                         --------------------------------------
                                              Paul Madera, a managing member

<PAGE>
                                                                  Page 54 of 229

                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                                September 16, 1999


                                                Accel VI L.P.
                                                By:  Accel VI Associates L.L.C.
                                                Its General Partner


                                                /s/ G. CARTER SEDNAOUI
                                                -------------------------------
                                                By: G. Carter Sednaoui
                                                Title: Managing Member


<PAGE>
                                                                  Page 55 of 229

                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                   September 16, 1999


                                   Accel Internet Fund II L.P.
                                   By:  Accel Internet Fund II Associates L.L.C.
                                   Its General Partner


                                   /s/ G. CARTER SEDNAOUI
                                   ---------------------------------------------
                                   By: G. Carter Sednaoui
                                   Title: Managing Member

<PAGE>
                                                                  Page 56 of 229

                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                        September 16, 1999


                                        Accel Keiretsu VI L.P.
                                        By:  Accel Keiretsu VI Associates L.L.C.
                                        Its General Partner


                                        /s/ G. CARTER SEDNAOUI
                                        ----------------------------------------
                                        By: G. Carter Sednaoui
                                        Title: Managing Member

<PAGE>
                                                                  Page 57 of 229

                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                        September 16, 1999


                                        Accel Investors '98 L.P.


                                        /s/ G. CARTER SEDNAOUI
                                        ---------------------------
                                        By: G. Carter Sednaoui
                                        Title: Managing Member
<PAGE>
                                                                  Page 58 of 229

                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                              September 16, 1999


                                              Brentwood Associates IX, L.P.
                                              By:  Brentwood IX Ventures, L.L.C.
                                              Its General Partner


                                              /s/ JOHN L. WALECKA
                                              ----------------------------------
                                              By: John L. Walecka
                                              Title: Managing Member

<PAGE>
                                                                  Page 59 of 229


                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                             September 16, 1999


                                             Brentwood Affiliates Fund III, L.P.
                                             By:  Brentwood IX Ventures, L.L.C.
                                             Its General Partner


                                             /s/ JOHN L. WALECKA
                                             -----------------------------------
                                             By: John L. Walecka
                                             Title: Managing Member


<PAGE>
                                                                  Page 60 of 229

                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                          September 16, 1999


                                          Worldview Technology Partners II, L.P.
                                          By:  Worldview Capital II, L.P.
                                          Its General Partner

                                          By:  Worldview Equity I, L.L.C.
                                          Its General Partner


                                          /s/ JAMES WEI
                                          --------------------------------------
                                          By: James Wei
                                          Title: Member

<PAGE>
                                                                  Page 61 of 229

                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                     September 16, 1999


                                     Worldview Technology International II, L.P.
                                     By:  Worldview Capital II, L.P.
                                     Its General Partner

                                     By:  Worldview Equity I, L.L.C.
                                     Its General Partner


                                     /s/ JAMES WEI
                                     ------------------------------------------
                                     By: James Wei
                                     Title: Member

<PAGE>
                                                                  Page 62 of 229

                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                          September 16, 1999


                                          Worldview Strategic Partners II, L.P.
                                          By:  Worldview Capital II, L.P.
                                          Its General Partner

                                          By:  Worldview Equity I, L.L.C.
                                          Its General Partner


                                          /s/ JAMES WEI
                                          -------------------------------------
                                          By: James Wei
                                          Title: Member

<PAGE>
                                                                  Page 63 of 229

                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                            September 16, 1999


                                            Bessemer Venture Partners IV L.P.
                                            By:  Deer IV & Co. LLC
                                            Its General Partner


                                            /s/ ROBERT H. BUESCHER
                                            ---------------------------------
                                            By: Robert H. Buescher
                                            Title: Manager

<PAGE>
                                                                  Page 64 of 229


                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                                     September 16, 1999


                                                     Bessec Ventures IV L.P.
                                                     By:  Deer IV & Co. LLC
                                                     Its General Partner


                                                     /s/ ROBERT H. BUESCHER
                                                     ---------------------------
                                                     By: Robert H. Buescher
                                                     Title: Manager

<PAGE>
                                                                  Page 65 of 229

                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                             September 16, 1999


                                             Cove Ventures, LLC
                                             By:  Cove Road Associates, LLC
                                             Its Managing Member


                                             /s/ ROBERT H. BUESCHER
                                             -----------------------------------
                                             By: Robert H. Buescher
                                             Title: Manager

<PAGE>
                                                                  Page 66 of 229


                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                            September 16, 1999


                                            Adams Capital Management, L.P.


                                            /s/ JOEL P. ADAMS
                                            ------------------------------------
                                            By: Joel P. Adams
                                            Title: General Partner

<PAGE>
                                                                  Page 67 of 229


                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                           September 16, 1999


                                           Columbia Capital ARTT Investors, LLC
                                           By:  Columbia Capital, L.L.C.
                                           Its Managing Member


                                           /s/ DONALD A. DOERING
                                           ------------------------------------
                                           By: Donald A. Doering
                                           Title: CFO

<PAGE>
                                                                  Page 68 of 229


                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                           September 16, 1999


                                           Columbia Capital ARTT Partners, LLC
                                           By:  Columbia Capital, L.L.C.
                                           Its Managing Member


                                           /s/ DONALD A. DOERING
                                           -----------------------------------
                                           By: Donald A. Doering
                                           Title: CFO

<PAGE>
                                                                  Page 69 of 229


                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                            September 16, 1999

                            GLOBAL PRIVATE EQUITY II - EUROPE
                            LIMITED PARTNERSHIP


                            GLOBAL PRIVATE EQUITY II - PGGM
                            LIMITED PARTNERSHIP


                            DIGITAL MEDIA AND COMMUNICATIONS
                            II LIMITED PARTNERSHIP


                            OAKSTONE VENTURES LIMITED
                            PARTNERSHIP


                            ADVENT CROWN FUND II C.V.


                            ADWEST LIMITED PARTNERSHIP

                            By:   Advent International Limited Partnership,
                                  General Partner
                            By:   Advent International Corporation,
                                  General Partner
                            By:   Janet L. Hennessy, Vice President*


                            ADVENT GLOBAL GECC LIMITED
                            PARTNERSHIP

                            By:   Advent Global Management Limited Partnership,
                                  General Partner
                            By:   Advent International Limited Partnership,
                                  General Partner
                            By:   Advent International Corporation,
                                  General Partner
                            By:   Janet L. Hennessy, Vice President*


                            ADVENT GLOBAL MANAGEMENT LIMITED PARTNERSHIP

                            By:   Advent International Limited Partnership,
                                  General Partner
                            By:   Advent International Corporation,
                                  General Partner
                            By:   Janet L. Hennessy, Vice President*

<PAGE>
                                                                  Page 70 of 229

                                      ADVENT PARTNERS LIMITED
                                      PARTNERSHIP

                                      By:   Advent International Corporation,
                                             General Partner
                                      By:   Janet L. Hennessy, Vice President*

                                      ADVENT INTERNATIONAL LIMITED PARTNERSHIP

                                      By:   Advent International Corporation,
                                            General Partner

                                      By:   Janet L. Hennessy, Vice President*

                                      ADVENT INTERNATIONAL CORPORATION

                                      By:   Janet L. Hennessy, Vice President*

                                      *For all of the above:

                                      /s/ JANET L. HENNESSY
                                      ----------------------------------------
                                      Janet L. Hennessy, Vice President

<PAGE>
                                                                  Page 71 of 229


                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                    September 16, 1999


                                    U.S. Telesource, Inc.


                                    /s/ MARC B. WEISBERG
                                    ------------------------------
                                    By: Marc B. Weisberg
                                    Title: President and Chief Executive Officer

<PAGE>
                                                                  Page 72 of 229


                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                            September 16, 1999


                            Qwest Communications Corporation

                            /s/ MARC B. WEISBERG
                            ------------------------------
                            By: Marc B. Weisberg
                            Title: Senior Vice President, Corporate Development

<PAGE>

                                                                  Page 73 of 229


                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                               September 16, 1999


                                               Qwest Corporation


                                               /s/ DRAKE S. TEMPEST
                                               --------------------------------
                                               By: Drake S. Tempest
                                               Title: Executive Vice President
                                                      and Counsel

<PAGE>
                                                                  Page 74 of 229


                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                         September 16, 1999


                                         Qwest Communications International Inc.



                                         /s/ DRAKE S. TEMPEST
                                         ---------------------------------------
                                         By:  Drake S. Tempest
                                         Title: Executive Vice President
                                                and General Counsel

<PAGE>
                                                                  Page 75 of 229


                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                    September 16, 1999


                                    Anschutz Company


                                    /s/ PHILIP F. ANSCHUTZ
                                    -------------------------------------------
                                    By: Philip F. Anschutz
                                    Title: Chairman and Chief Executive Officer

<PAGE>
                                                                  Page 76 of 229


                                    SIGNATURE

         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                             September 16, 1999


                                             Philip F. Anschutz


                                             /s/ PHILIP F. ANSCHUTZ
                                             ---------------------------


                                                                  Page 77 of 229

                                    EXHIBIT A
                             JOINT FILING STATEMENT

The undersigned acknowledge and agree that the foregoing Statement on Schedule
13D is filed on behalf of each of the undersigned and that all subsequent
amendments to such Statement on Schedule 13D may be filed on behalf of each of
the undersigned without the necessity of filing additional joint filing
statements. The undersigned acknowledge that each of them will be responsible
for the timely filing of such amendments, and for the completeness and accuracy
of the information concerning it contained herein and therein, but will not be
responsible for the completeness and accuracy of the information concerning the
others of them, except to the extent that it knows or has reason to believe that
such information is inaccurate.

                             September 16, 1999

                             Oak Investment Partners VIII, Limited Partnership
                             By:  Oak Associates VIII, LLC
                             Its General Partner


                             /s/  BANDEL CARANO
                             -------------------------------------------------
                             By:  Bandel Carano
                             Title: General Partner

<PAGE>
                                                                  Page 78 of 229


                                    Oak VIII Affiliate Fund, Limited Partnership
                                    By:  Oak VIII Affiliates, LLC
                                    Its General Partner


                                    /s/ BANDEL CARANO
                                    --------------------------------------------
                                    By: Bandel Carano
                                    Title: General Partner

<PAGE>
                                                                  Page 79 of 229

                                   MeriTech Capital Partners L.P.
                                   By:    MeriTech Capital Associates L.L.C.
                                          its General Partner
                                   By:    MeriTech Management Associates L.L.C.
                                          a managing member


                                   By:    /s/ PAUL MADERA
                                      -----------------------------------------
                                              Paul Madera, a managing member



                                   MeriTech Capital Affiliates L.P.
                                   By:    Meritech Capital Associates L.L.C.
                                          its General Partner
                                   By:    MeriTech Management Associates L.L.C.
                                          a managing member


                                   By:    /s/ PAUL MADERA
                                      -----------------------------------------
                                              Paul Madera, a managing member

<PAGE>
                                                                  Page 80 of 229


                                                  Accel VI L.P.
                                                  By: Accel VI Associates L.L.C.
                                                  Its General Partner


                                                  /s/  G. CARTER SEDNAOUI
                                                  ------------------------------
                                                  By:  G. Carter Sednaoui
                                                  Title:  Managing Member

<PAGE>
                                                                  Page 81 of 229


                                  Accel Internet Fund II L.P.
                                  By: Accel Internet Fund II Associates L.L.C.
                                  Its General Partner


                                  /s/  G. CARTER SEDNAOUI
                                  --------------------------------------------
                                  By:  G. Carter Sednaoui
                                  Title:  Managing Member

<PAGE>
                                                                  Page 82 of 229


                                       Accel Keiretsu VI L.P.
                                       By: Accel Keiretsu VI Associates L.L.C.
                                       Its General Partner


                                       /s/  G. CARTER SEDNAOUI
                                       ---------------------------------------
                                       By:  G. Carter Sednaoui
                                       Title:  Managing Member

<PAGE>
                                                                  Page 83 of 229


                                                     Accel Investors '98 L.P.


                                                     /s/  G. CARTER SEDNAOUI
                                                     ------------------------
                                                     By:  G. Carter Sednaoui
                                                     Title:  Managing Member

<PAGE>

                                                                  Page 84 of 229

                                              Brentwood Associates IX, L.P.
                                              By: Brentwood IX Ventures, L.L.C.
                                              Its General Partner


                                              /s/ JOHN L. WALECKA
                                              ---------------------------------
                                              By: John L. Walecka
                                              Title:  Managing Member

<PAGE>
                                                                  Page 85 of 229


                                           Brentwood Affiliates Fund III, L.P.
                                           By:  Brentwood IX Ventures, L.L.C.
                                           Its  General Partner


                                           /s/  JOHN L. WALECKA
                                           -----------------------------------
                                           By:  John L. Walecka
                                           Title:  Managing Member

<PAGE>
                                                                  Page 86 of 229


                                    Worldview Technology Partners, II, L.P.
                                    By: Worldview Capital II, L.P.
                                    Its General Partner

                                    By: Worldview Equity I, L.L.C.
                                    Its General Partner


                                    /s/ JAMES WEI
                                    ---------------------------------------
                                    By: James Wei
                                    Title:  Member

<PAGE>
                                                                  Page 87 of 229


                                    Worldview Technology International, II, L.P.
                                    By: Worldview Capital II, L.P.
                                    Its General Partner

                                    By:  Worldview Equity I, L.L.C.
                                    Its General Partner


                                    /s/ JAMES WEI
                                    --------------------------------------------
                                    By: James Wei
                                    Title: Member

<PAGE>
                                                                  Page 88 of 229


                                    Worldview Strategic Partners, II, L.P.
                                    By: Worldview Capital II, L.P.
                                    Its General Partner

                                    By: Worldview Equity I, L.L.C.
                                    Its General Partner


                                    /s/ JAMES WEI
                                    --------------------------------------------
                                    By: James Wei
                                    Title:  Member

<PAGE>

                                                                  Page 89 of 229

                                    Bessemer Venture Partners IV L.P.
                                    By: Deer IV & Co. LLC
                                    Its General Partner


                                    /s/  ROBERT H. BUESCHER
                                    --------------------------------------------
                                    By:  Robert H. Buescher
                                    Title:  Manager

<PAGE>
                                                                  Page 90 of 229


                                    Bessec Ventures IV L.P.
                                    By: Deer IV & Co. LLC
                                    Its General Partner


                                    /s/ ROBERT H. BUESCHER
                                    --------------------------------------------
                                    By: Robert H. Buescher
                                    Title:  Manager

<PAGE>

                                                                  Page 91 of 229

                                           Cove Ventures, LLC
                                           By: Cove Road Associates, LLC
                                           Its Managing Member


                                           /s/  ROBERT H. BUESCHER
                                           -------------------------------------
                                           By:  Robert H. Buescher
                                           Title:  Attorney-in-fact

<PAGE>
                                                                  Page 92 of 229


                                            Adams Capital Management, L.P.


                                            /s/ JOEL P. ADAMS
                                            ------------------------------
                                            By: Joel P. Adams
                                            Title: General Partner

<PAGE>

                                                                  Page 93 of 229


                                            Columbia Capital ARTT Investors, LLC
                                            By: Columbia Capital, L.L.C.
                                            Its Managing Member


                                            /s/ DONALD A. DOERING
                                            ------------------------------------
                                            By: Donald A. Doering
                                            Title: CFO

<PAGE>
                                                                  Page 94 of 229


                                            Columbia Capital ARTT Partners, LLC
                                            By: Columbia Capital, L.L.C.
                                            Its Managing Member


                                            /s/ DONALD A. DOERING
                                            -----------------------------------
                                            By: Donald A. Doering
                                            Title:  CFO

<PAGE>
                                                                  Page 95 of 229


                             GLOBAL PRIVATE EQUITY II - EUROPE
                             LIMITED PARTNERSHIP


                             GLOBAL PRIVATE EQUITY II - PGGM
                             LIMITED PARTNERSHIP


                             DIGITAL MEDIA AND COMMUNICATIONS
                             II LIMITED PARTNERSHIP


                             OAKSTONE VENTURES LIMITED
                             PARTNERSHIP


                             ADVENT CROWN FUND II C.V.


                             ADWEST LIMITED PARTNERSHIP

                             By:   Advent International Limited Partnership,
                                   General Partner
                             By:   Advent International Corporation,
                                   General Partner
                             By:   Janet L. Hennessy, Vice President*

                             ADVENT GLOBAL GECC LIMITED
                             PARTNERSHIP

                             By:   Advent Global Management Limited Partnership,
                                   General Partner
                             By:   Advent International Limited Partnership,
                                   General Partner
                             By:   Advent International Corporation,
                                   General Partner
                             By:   Janet L. Hennessy, Vice President*

                             ADVENT GLOBAL MANAGEMENT LIMITED PARTNERSHIP

                             By:   Advent International Limited Partnership,
                                   General Partner
                             By:   Advent International Corporation,
                                   General Partner
                             By:   Janet L. Hennessy, Vice President*


<PAGE>

                                                                  Page 96 of 229

                                     ADVENT PARTNERS LIMITED
                                     PARTNERSHIP
                                     By:   Advent International Corporation,
                                            General Partner
                                     By:   Janet L. Hennessy, Vice President*

                                     ADVENT INTERNATIONAL LIMITED PARTNERSHIP

                                     By:   Advent International Corporation,
                                           General Partner

                                     By:   Janet L. Hennessy, Vice President*

                                     ADVENT INTERNATIONAL CORPORATION

                                     By:   Janet L. Hennessy, Vice President*

                                     *For all of the above:

                                     /s/ JANET L. HENNESSY
                                     ----------------------------------------
                                     Janet L. Hennessy, Vice President

<PAGE>
                                                                  Page 97 of 229


                                   U.S. Telesource, Inc.


                                   /s/ MARC B. WEISBERG
                                   ---------------------------------------------
                                   By: Marc B. Weisberg
                                   Title:  President and Chief Executive Officer

<PAGE>

                                                                  Page 98 of 229

                         Qwest Communications Corporation

                         /s/ MARC B. WEISBERG
                         ----------------------------------------------------
                         By: Marc B. Weisberg
                         Title:  Senior Vice President, Corporate Development

<PAGE>

                                                                  Page 99 of 229

                                          Qwest Corporation


                                          /s/ DRAKE S. TEMPEST
                                          --------------------------------
                                          By: Drake S. Tempest
                                          Title:  Executive Vice President
                                                  and General Counsel

<PAGE>

                                                                 Page 100 of 229

                                      Qwest Communications International Inc.


                                      /s/ DRAKE S. TEMPEST
                                      --------------------------------
                                      By: Drake S. Tempest
                                      Title:  Executive Vice President
                                              and General Counsel

<PAGE>
                                                                 Page 101 of 229


                                    Anschutz Company


                                    /s/ PHILIP F. ANSCHUTZ
                                    -------------------------------------------
                                    By:  Philip F. Anschutz
                                    Title: Chairman and Chief Executive Officer

<PAGE>

                                                                 Page 102 of 229

                                    Philip F. Anschutz


                                    /s/  PHILIP F. ANSCHUTZ
                                    --------------------------------------------


<TABLE>
<CAPTION>
                                                                 Page 103 of 229

                                    EXHIBIT B

                    Control Parties for Each Reporting Person

                                                 Present Principal Occupation,
                                                 Name, Address and Principal
Name, Business Address           Citizenship     Business of Organization
- ----------------------           -----------     -----------------------------
<S>                             <C>              <C>
OIP                                              General Partner
                                                 Oak Investment partners VIII, Limited
Frederic W. Harman               U.S.            Partnership
525 University Avenue                            525 University Avenue
Suite 1300                                       Suite 1300
Palo Alto, CA 94301                              Palo Alto, CA 94301
                                                 Venture Capital Investment

Bandel L. Carano                 U.S.            General Partner
525 University Avenue                            Oak Investment partners VIII, Limited
Suite 1300                                       Partnership
Palo Alto, CA 94301                              525 University Avenue
                                                 Suite 1300
                                                 Palo Alto, CA 94301
                                                 Venture Capital Investment

Edward F. Glassmeyer             U.S.            General Partner
525 University Avenue                            Oak Investment partners VIII, Limited
Suite 1300                                       Partnership
Palo Alto, CA 94301                              525 University Avenue
                                                 Suite 1300
                                                 Palo Alto, CA 94301
                                                 Venture Capital Investment

Ann Lamont                       U.S.            General Partner
525 University Avenue                            Oak Investment partners VIII, Limited
Suite 1300                                       Partnership
Palo Alto, CA 94301                              525 University Avenue
                                                 Suite 1300
                                                 Palo Alto, CA 94301
                                                 Venture Capital Investment
</TABLE>

<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 104 of 229

                                                 Present Principal Occupation,
                                                 Name, Address and Principal
Name, Business Address           Citizenship     Business of Organization
- ----------------------           -----------     -----------------------------
<S>                             <C>              <C>
Gerald Gallagher                 U.S.            General Partner
525 University Avenue                            Oak Investment partners VIII, Limited
Suite 1300                                       Partnership
Palo Alto, CA 94301                              525 University Avenue
                                                 Suite 1300
                                                 Palo Alto, CA 94301
                                                 Venture Capital Investment

OAF
- ---

Frederic W. Harman               U.S.            General Partner
525 University Avenue                            Oak Investment partners VIII, Limited
Suite 1300                                       Partnership
Palo Alto, CA 94301                              525 University Avenue
                                                 Ste 1300
                                                 Palo Alto, CA 94301
                                                 Venture Capital Investment

Bandel L. Carano                 U.S.            General Partner
525 University Avenue                            Oak Investment partners VIII, Limited
Suite 1300                                       Partnership
Palo Alto, CA 94301                              525 University Avenue
                                                 Suite 1300
                                                 Palo Alto, CA 94301
                                                 Venture Capital Investment

Edward F. Glassmeyer             U.S.            General Partner
525 University Avenue                            Oak Investment partners VIII, Limited
Suite 1300                                       Partnership
Palo Alto, CA 94301                              525 University Avenue
                                                 Suite 1300
                                                 Palo Alto, CA 94301
                                                 Venture Capital Investment
</TABLE>

<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 105 of 229

                                                      Present Principal Occupation,
                                                      Name, Address and Principal
Name, Business Address                Citizenship     Business of Organization
- ----------------------                -----------     -----------------------------
<S>                                 <C>              <C>
Ann Lamont                            U.S.            General Partner
525 University Avenue                                 Oak Investment partners VIII, Limited
Suite 1300                                            Partnership
Palo Alto, CA 94301                                   525 University Avenue
                                                      Ste 1300
                                                      Palo Alto, CA 94301
                                                      Venture Capital Investment

Gerald Gallagher                      U.S.            General Partner
525 University Avenue                                 Oak Investment partners VIII, Limited
Suite 1300                                            Partnership
Palo Alto, CA 94301                                   525 University Avenue
                                                      Suite 1300
                                                      Palo Alto, CA 94301
                                                      Venture Capital Investment

CAP
- ---

MeriTech Capital Associates LLC       Delaware        General Partner
428 University Avenue                                 MeriTech Capital Partners, L.P.
Palo Alto, CA  94301                                  428 University Avenue
                                                      Palo Alto, California  94301
                                                      Venture Capital Management

MeriTech Management Associates, LLC   Delaware        Managing Member
428 University Avenue                                 MeriTech Capital Associates LLC
Palo Alto, CA  94301                                  428 University Avenue
                                                      Palo Alto, CA 94301
                                                      Venture Capital Management

Paul S. Madera                        U.S.            Managing Member
428 University Avenue                                 MeriTech Capital Associates LLC
Palo Alto, CA  94301                                  428 University Avenue
                                                      Palo Alto, CA 94301
                                                      Venture Capital Management
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 106 of 229



                                                     Present Principal Occupation,
                                                     Name, Address and Principal
Name, Business Address               Citizenship     Business of Organization
- ----------------------               -----------     -----------------------------
<S>                                 <C>              <C>
Michael B. Gordon                    U.S.            Managing Member
428 University Avenue                                MeriTech Capital Associates LLC
Palo Alto, CA  94301                                 428 University Avenue
                                                     Palo Alto, CA 94301
                                                     Venture Capital Management

AFFILIATES
- ----------

MeriTech Capital Associates LLC      Delaware        General Partner
428 University Avenue                                MeriTech Capital Partners, L.P.
Palo Alto, CA  94301                                 428 University Avenue
                                                     Palo Alto, California  94301
                                                     Venture Capital Management

Management Member                    Delaware        Managing Member
MeriTech Capital Associates LLC                      MeriTech Capital Associates LLC
428 University Avenue                                428 University Avenue
Palo Alto, CA  94301                                 Palo Alto, CA  94301
Venture Capital Management                           Venture Capital Management

ACCEL VI
- --------

Accel VI Associates L.L.C.           Delaware        General Partner
c/o Accel Partners                                   Accel VI L.P.
428 University Avenue                                428 University Avenue
Palo Alto, CA  94301                                 Palo Alto, CA 94301
                                                     Venture Capital Investment

Arthur C. Patterson                  U.S.            Managing Member
c/o Accel Partners                                   Accel VI Associates L.L.C.
428 University Avenue                                428 University Avenue
Palo Alto, CA  94301                                 Palo Alto, CA 94301
                                                     Venture Capital Investment

ACP Family Partnership L.P.          California      Managing Member
c/o Accel Partners                                   Accel VI Associates L.L.C.
428 University Avenue                                428 University Avenue
Palo Alto, CA  94301                                 Palo Alto, CA 94301
                                                     Venture Capital Investment
</TABLE>

<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 107 of 229


                                                        Present Principal Occupation,
                                                        Name, Address and Principal
Name, Business Address                  Citizenship     Business of Organization
- ----------------------                  -----------     -----------------------------
<S>                                   <C>              <C>
James R. Swartz                         U.S.            Managing Member
c/o Accel Partners                                      Accel VI Associates L.L.C.
428 University Avenue                                   428 University Avenue
Palo Alto, CA  94301                                    Palo Alto, CA 94301
                                                        Venture Capital Investment

James W. Breyer                         U.S.            Managing Member
c/o Accel Partners                                      Accel VI Associates L.L.C.
428 University Avenue                                   428 University Avenue
Palo Alto, CA  94301                                    Palo Alto, CA 94301
                                                        Venture Capital Investment

The Breyer 1995 Trust dated 10/4/95     California      Managing Member
c/o Accel Partners                                      Accel VI Associates L.L.C.
428 University Avenue                                   428 University Avenue
Palo Alto, CA 94301                                     Palo Alto, CA 94301
                                                        Venture Capital Investment

Swartz Family Partnership L.P.          Delaware        Managing Member
c/o Accel Partners                                      Accel VI Associates L.L.C.
428 University Avenue                                   428 University Avenue
Palo Alto, CA  94301                                    Palo Alto, CA 94301
                                                        Venture Capital Investment

J. Peter Wagner                         U.S.            Managing Member
c/o Accel Partners                                      Accel VI Associates L.L.C.
428 University Avenue                                   428 University Avenue
Palo Alto, CA  94301                                    Palo Alto, CA 94301
                                                        Venture Capital Investment

G. Carter Sednaoui                      U.S.            Managing Member
c/o Accel Partners                                      Accel VI Associates L.L.C.
428 University Avenue                                   428 University Avenue
Palo Alto, CA  94301                                    Palo Alto, CA 94301
                                                        Venture Capital Investment
</TABLE>

<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 108 of 229


                                                           Present Principal Occupation,
                                                           Name, Address and Principal
Name, Business Address                     Citizenship     Business of Organization
- ----------------------                     -----------     -----------------------------
<S>                                       <C>              <C>
ACCEL INTERNET
- --------------

Accel Internet Fund II Associates L.L.C.   Delaware        General Partner
c/o Accel Partners                                         Accel Internet Fund L.P. II
428 University Avenue                                      428 University Avenue
Palo Alto, CA  94301                                       Palo Alto, CA 94301
                                                           Venture Capital Investment

Arthur C. Patterson                        U.S.            Managing Member
c/o Accel Partners                                         Accel Internet Fund II Associates L.L.C.
428 University Avenue                                      428 University Avenue
Palo Alto, CA  94301                                       Palo Alto, CA 94301
                                                           Venture Capital Investment

James R. Swartz                            U.S.            Managing Member
c/o Accel Partners                                         Accel Internet Fund II Associates L.L.C.
428 University Avenue                                      428 University Avenue
Palo Alto, CA  94301                                       Palo Alto, CA 94301
                                                           Venture Capital Investment

James W. Breyer                            U.S.            Managing Member
c/o Accel Partners                                         Accel Internet Fund II Associates L.L.C.
428 University Avenue                                      428 University Avenue
Palo Alto, CA  94301                                       Palo Alto, CA 94301
                                                           Venture Capital Investment

Swartz Family Partnership L.P.             Delaware        Managing Member
c/o Accel Partners                                         Accel Internet Fund II Associates L.L.C.
428 University Avenue                                      428 University Avenue
Palo Alto, CA  94301                                       Palo Alto, CA 94301
                                                           Venture Capital Investment

J. Peter Wagner                            U.S.            Managing Member
c/o Accel Partners                                         Accel Internet Fund II Associates L.L.C.
428 University Avenue                                      428 University Avenue
Palo Alto, CA  94301                                       Palo Alto, CA 94301
                                                           Venture Capital Investment
</TABLE>

<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 109 of 229


                                                       Present Principal Occupation,
                                                       Name, Address and Principal
Name, Business Address                 Citizenship     Business of Organization
- ----------------------                 -----------     -----------------------------
<S>                                    <C>              <C>
G. Carter Sednaoui                     U.S.            Managing Member
c/o Accel Partners                                     Accel Internet Fund II Associates L.L.C.
428 University Avenue                                  428 University Avenue
Palo Alto, CA  94301                                   Palo Alto, CA 94301
                                                       Venture Capital Investment
ACCEL KEIRETSU
- --------------

Accel Keiretsu VI Associates L.L.C.    Delaware        General Partner
c/o Accel Partners                                     Accel Keiretsu VI L.P.
428 University Avenue                                  428 University Avenue
Palo Alto, CA  94301                                   Palo Alto, CA 94301
                                                       Venture Capital Investment

Arthur C. Patterson                    U.S.            Managing Member
c/o Accel Partners                                     Accel Keiretsu VI Associates L.L.C.
428 University Avenue                                  428 University Avenue
Palo Alto, CA  94301                                   Palo Alto, CA 94301
                                                       Venture Capital Investment

James R. Swartz                        U.S.            Managing Member
c/o Accel Partners                                     Accel Keiretsu VI Associates L.L.C.
428 University Avenue                                  428 University Avenue
Palo Alto, CA  94301                                   Palo Alto, CA 94301
                                                       Venture Capital Investment

James W. Breyer                        U.S.            Managing Member
c/o Accel Partners                                     Accel Keiretsu VI Associates L.L.C.
428 University Avenue                                  428 University Avenue
Palo Alto, CA  94301                                   Palo Alto, CA 94301
                                                       Venture Capital Investment

J. Peter Wagner                        U.S.            Managing Member
c/o Accel Partners                                     Accel Keiretsu VI Associates L.L.C.
428 University Avenue                                  428 University Avenue
Palo Alto, CA  94301                                   Palo Alto, CA 94301
                                                       Venture Capital Investment
</TABLE>

<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 110 of 229

                                                       Present Principal Occupation,
                                                       Name, Address and Principal
Name, Business Address                 Citizenship     Business of Organization
- ----------------------                 -----------     -----------------------------
<S>                                    <C>              <C>
G. Carter Sednaoui                     U.S.            Managing Member
c/o Accel Partners                                     Accel Keiretsu VI Associates L.L.C.
428 University Avenue                                  428 University Avenue
Palo Alto, CA  94301                                   Palo Alto, CA 94301
                                                       Venture Capital Investment
ACCEL INVESTORS
- ---------------

Arthur C. Patterson                    U.S.            General Partner
c/o Accel Partners                                     Accel Investors '98 L.P.
428 University Avenue                                  428 University Avenue
Palo Alto, CA  94301                                   Palo Alto, CA 94301
                                                       Venture Capital Investment

James R. Swartz                        U.S.            General Partner
c/o Accel Partners                                     Accel Investors '98 L.P.
428 University Avenue                                  428 University Avenue
Palo Alto, CA  94301                                   Palo Alto, CA 94301
                                                       Venture Capital Investment

James W. Breyer                        U.S.            General Partner
c/o Accel Partners                                     Accel Investors '98 L.P.
428 University Avenue                                  428 University Avenue
Palo Alto, CA  94301                                   Palo Alto, CA 94301
                                                       Venture Capital Investment

J. Peter Wagner                        U.S.            General Partner
c/o Accel Partners                                     Accel Investors '98 L.P.
428 University Avenue                                  428 University Avenue
Palo Alto, CA  94301                                   Palo Alto, CA 94301
                                                       Venture Capital Investment

G. Carter Sednaoui                     U.S.            General Partner
c/o Accel Partners                                     Accel Investors '98 L.P.
428 University Avenue                                  428 University Avenue
Palo Alto, CA  94301                                   Palo Alto, CA 94301
                                                       Venture Capital Investment
</TABLE>

<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 111 of 229

                                                       Present Principal Occupation,
                                                       Name, Address and Principal
Name, Business Address                 Citizenship     Business of Organization
- ----------------------                 -----------     -----------------------------
<S>                                    <C>              <C>
BRENTWOOD IX
- ------------

Brentwood IX Ventures, L.L.C.          U.S.            General Partner
3000 Sand Hill Road                                    Brentwood Associates IX, L.P.
Bldg. 1, Suite 260                                     3000 Sand Hill Road, Bldg. 1, Suite 260
Menlo Park, CA  94025                                  Menlo Park, CA  94025
                                                       Venture Capital Investment

Jeffrey D. Brody                       U.S.            General Partner
3000 Sand Hill Road                                    Brentwood Associates IX, L.P.
Bldg. 1, Suite 260                                     3000 Sand Hill Road, Bldg. 1, Suite 260
Menlo Park, CA  94025                                  Menlo Park, CA  94025
                                                       Venture Capital Investment

John L. Walecka                        U.S.            General Partner
3000 Sand Hill Road                                    Brentwood Associates IX, L.P.
Bldg. 1, Suite 260                                     3000 Sand Hill Road, Bldg. 1, Suite 260
Menlo Park, CA  94025                                  Menlo Park, CA  94025
                                                       Venture Capital Investment

Brian G. Atwood                        U.S.            Managing Member
3000 Sand Hill Road                                    Brentwood IX Ventures, L.L.C.
Bldg. 1, Suite 260                                     General Partner
Menlo Park, CA  94025                                  Brentwood Venture Capital
                                                       3000 Sand Hill Road, Bldg. 1, Suite 260
                                                       Menlo Park, CA 94025
                                                       Venture Capital Investment

William J. Link                        U.S.            Managing Member
3000 Sand Hill Road                                    Brentwood IX Ventures, L.L.C.
Bldg. 1, Suite 260                                     General Partner
Menlo Park, CA  94025                                  Brentwood Venture Capital
                                                       3000 Sand Hill Road, Bldg. 1, Suite 260
                                                       Menlo Park, CA 94025
                                                       Venture Capital Investment
</TABLE>

<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 112 of 229

                                                       Present Principal Occupation,
                                                       Name, Address and Principal
Name, Business Address                 Citizenship     Business of Organization
- ----------------------                 -----------     -----------------------------
<S>                                    <C>              <C>
Ross A. Jaffe                          U.S.            Managing Member
3000 Sand Hill Road                                    Brentwood IX Ventures, L.L.C.
Bldg. 1, Suite 260                                     General Partner
Menlo Park, CA  94025                                  Brentwood Venture Capital
                                                       3000 Sand Hill Road, Bldg. 1, Suite 260
                                                       Menlo Park, CA 94025
                                                       Venture Capital Investment

G. Bradford Jones                      U.S.            Managing Member
3000 Sand Hill Road                                    Brentwood IX Ventures, L.L.C.
Menlo Park, CA  94025                                  General Partner
                                                       Brentwood Venture Capital
                                                       525 University Avenue
                                                       Ste 1300
                                                       Palo Alto, CA 94301
                                                       Venture Capital Investment

BRENTWOOD III
- -------------

Brentwood IX Ventures, L.L.C.          U.S.            General Partner
3000 Sand Hill Road                                    Brentwood Affiliates Fund III, L.P.
Bldg 1, Suite 260                                      3000 Sand Hill Road
Menlo Park, CA  94025                                  Menlo Park, CA  94025
                                                       Venture Capital Investment

Jeffrey D. Brody                       U.S.            Managing Member
3000 Sand Hill Road                                    Brentwood IX Ventures, L.L.C. and
Bldg 1, Suite 260                                      General Partner
Menlo Park, CA  94025                                  Brentwood Venture Capital
                                                       3000 Sand Hill Road
                                                       Menlo Park, CA 94025
                                                       Venture Capital Investment

John L. Walecka                        U.S.            Managing Member
3000 Sand Hill Road                                    Brentwood IX Ventures, L.L.C. and General
Bldg 1, Suite 260                                      Partner
Menlo Park, CA  94025                                  Brentwood Venture Capital
                                                       3000 Sand Hill Road
                                                       Menlo Park, CA 94025
                                                       Venture Capital Investment
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 113 of 229


                                                     Present Principal Occupation,
                                                     Name, Address and Principal
Name, Business Address               Citizenship     Business of Organization
- ----------------------               -----------     -----------------------------
<S>                                 <C>              <C>
Brian G. Atwood                      U.S.            Managing Member
3000 Sand Hill Road                                  Brentwood IX Ventures, L.L.C. and
Bldg 1, Suite 260                                    General Partner
Menlo Park, CA  94025                                Brentwood Venture Capital
                                                     3000 Sand Hill Road
                                                     Menlo Park, CA 94025
                                                     Venture Capital Investment

William J. Link                      U.S.            Managing Member
3000 Sand Hill Road                                  Brentwood IX Ventures, L.L.C. and General
Bldg 1, Suite 260                                    Partner
Menlo Park, CA  94025                                Brentwood Venture Capital
                                                     3000 Sand Hill Road
                                                     Menlo Park, CA 94025
                                                     Venture Capital Investment

Ross A. Jaffe                        U.S.            Managing Member
3000 Sand Hill Road                                  Brentwood IX Ventures, L.L.C. and General
Bldg 1, Suite 260                                    Partner
Menlo Park, CA  94025                                Brentwood Venture Capital
                                                     3000 Sand Hill Road
                                                     Menlo Park, CA 94025
                                                     Venture Capital Investment

G. Bradford Jones                    U.S.            Managing Member
3000 Sand Hill Road                                  Brentwood IX Ventures, L.L.C. and General
Bldg 1, Suite 260                                    Partner
Menlo Park, CA  94025                                Brentwood Venture Capital
                                                     3000 Sand Hill Road
                                                     Menlo Park, CA 94025
                                                     Venture Capital Investment
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 114 of 229


                                                     Present Principal Occupation,
                                                     Name, Address and Principal
Name, Business Address               Citizenship     Business of Organization
- ----------------------               -----------     -----------------------------
<S>                                 <C>              <C>
WTP
- ---

Worldview Capital II, L.P.           Delaware        General Partner
435 Tasso, Suite 120                                 Worldview Technology Partners II, L.P.
Palo Alto, CA  94301                                 435 Tasso, Suite 120
                                                     Palo Alto, CA 94301
                                                     Venture Capital Investment

James Wei                            Canadian        Worldview Technology Partners II, L.P.
435 Tasso, Suite 120                                 and Chief Technology Officer
Palo Alto, CA  94301                                 Worldview Management Corporation
                                                     435 Tasso, Suite 120
                                                     Palo Alto, CA 94301
                                                     Venture Capital

Michael Orsak                        U.S.            General Partner
435 Tasso, Suite 120                                 Worldview Technology Partners II, L.P.
Palo Alto, CA  94301                                 and President
                                                     Worldview Management Corporation
                                                     435 Tasso, Suite 120
                                                     Palo Alto, CA 94301
                                                     Venture Capital

John Boyle                           U.S.            General Partner
435 Tasso, Suite 120                                 Worldview Technology Partners II, L.P.
Palo Alto, CA  94301                                 435 Tasso, Suite 120
                                                     Palo Alto, CA 94301
                                                     Venture Capital

Susumu Tanaka                        Japanese        General Partner
435 Tasso, Suite 120                                 General Partner
Palo Alto, CA  94301                                 Worldview Technology Partners II, L.P.
                                                     435 Tasso, Suite 120
                                                     Palo Alto, CA 94301
                                                     Venture Capital
</TABLE>

<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 115 of 229

                                                     Present Principal Occupation,
                                                     Name, Address and Principal
Name, Business Address               Citizenship     Business of Organization
- ----------------------               -----------     -----------------------------
<S>                                 <C>              <C>
WTI
- ---

Worldview Capital II, L.P.           Delaware        General Partner
435 Tasso, Suite 120                                 Worldview Technology Partners II, L.P.
Palo Alto, CA  94301                                 435 Tasso, Suite 120
                                                     Palo Alto, CA 94301
                                                     Venture Capital Investment

James Wei                            Canadian        General Partner
435 Tasso, Suite 120                                 Worldview Capital II, L.P. and Chief
Palo Alto, CA  94301                                 Technology Officer
                                                     Worldview Management Corporation
                                                     435 Tasso, Suite 120
                                                     Palo Alto, CA 94301
                                                     Venture Capital

Michael Orsak                        U.S.            General Partner Worldview Capital II,
435 Tasso, Suite 120                                 L.P. and President
Palo Alto, CA  94301                                 Worldview Management Corporation
                                                     435 Tasso, Suite 120
                                                     Palo Alto, CA 94301
                                                     Venture Capital

John Boyle                           U.S.            General Partner Worldview Capital II,
435 Tasso, Suite 120                                 L.P.
Palo Alto, CA  94301                                 435 Tasso, Suite 120
                                                     Palo Alto, CA  94301
                                                     Venture Capital

Susumu Tanaka                        Japanese        General Partner Worldview Capital II,
435 Tasso, Suite 120                                 L.P.
Palo Alto, CA  94301                                 435 Tasso, Suite 120
                                                     Palo Alto, CA  94301
                                                     Venture Capital
</TABLE>

<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 116 of 229

                                                     Present Principal Occupation,
                                                     Name, Address and Principal
Name, Business Address               Citizenship     Business of Organization
- ----------------------               -----------     -----------------------------
<S>                                 <C>              <C>
WSP
- ---

Worldview Capital II, L.P.           Delaware        General Partner
435 Tasso, Suite 120                                 Worldview Technology Partners II, L.P.
Palo Alto, CA  94301                                 435 Tasso, Suite 120
                                                     Palo Alto, CA 94301
                                                     Venture Capital Investment

James Wei                            Canadian        General Partner Worldview Capital II,
435 Tasso, Suite 120                                 L.P. and Chief Technology Officer
Palo Alto, CA  94301                                 Worldview Management Corporation
                                                     435 Tasso, Suite 120
                                                     Palo Alto, CA 94301
                                                     Venture Capital

Michael Orsak                        U.S.            General Partner Worldview Capital II, L.P. and
435 Tasso, Suite 120                                 Vice President
Palo Alto, CA  94301                                 Worldview Management Corporation
                                                     435 Tasso, Suite 120
                                                     Palo Alto, CA 94301
                                                     Venture Capital

John Boyle                           U.S.            General Partner Worldview Capital II, L.P.
435 Tasso, Suite 120                                 435 Tasso, Suite 120
Palo Alto, CA  94301                                 Palo Alto, CA  94301
                                                     Venture Capital

Susumu Tanaka                        Japanese        General Partner Worldview Capital II, L.P.
435 Tasso, Suite 120                                 435 Tasso, Suite 120
Palo Alto, CA  94301                                 Palo Alto, CA  94301
                                                     Venture Capital
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 117 of 229


                                                Present Principal Occupation,
                                                Name, Address and Principal
Name, Business Address          Citizenship     Business of Organization
- ----------------------          -----------     -----------------------------
<S>                            <C>              <C>
BESSEMER
- --------

Deer IV & Co. LLC               Delaware        General Partner
1400 Old Country Road                           Bessemer Venture
Suite 407                                         Partner IV L.P.
Westbury, NY  11590                             1400 Old Country Road
                                                Suite 407
                                                Westbury, NY 11590
                                                Venture Capital Investment

William T. Burgin               U.S.            Manager
1400 Old Country Road                           Deer IV & Co. LLC
Suite 407                                       83 Walnut Street
Westbury, NY  11590                             Wellesley Hills, MA 02481
                                                Venture Capital Investment

Robert H. Buescher              U.S.            Manager
1400 Old Country Road                           Deer IV & Co. LLC
Suite 407                                       1400 Old Country Road
Westbury, NY  11590                             Suite 407
                                                Westbury, NY 11590
                                                Venture Capital Investment

David J. Cowan                  U.S.            Manager
1400 Old Country Road                           Deer IV & Co. LLC
Suite 407                                       1400 Old Country Road
Westbury, NY  11590                             Suite 407
                                                Westbury, NY 11590
                                                Venture Capital Investment

G. Felda Hardymon               U.S.            Manager
1400 Old Country Road                           Deer IV & Co. LLC
Suite 407                                       1400 Old Country Road
Westbury, NY  11590                             Suite 407
                                                Westbury, NY 11590
                                                Venture Capital Investment
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 118 of 229


                                                Present Principal Occupation,
                                                Name, Address and Principal
Name, Business Address          Citizenship     Business of Organization
- ----------------------          -----------     -----------------------------
<S>                            <C>              <C>
Christopher F.O. Gabrieli       U.S.            Manager
1400 Old Country Road                           Deer IV & Co. LLC
Suite 407                                       83 Walnut Street
Westbury, NY  11590                             Wellesley Hills, MA 02481
                                                Venture Capital Investment

Robi L. Soni                    U.S.            Manager
1400 Old Country Road                           Deer IV & Co. LLC
Suite 407                                       83 Walnut Street
Westbury, NY  11590                             Wellesley Hills, MA 02481
                                                Venture Capital Investment

Robert P. Goodman               U.S.            Member, Deer IV & Co. LLC
1400 Old Country Road                           Managing Member
Suite 407                                       Cove Road Associates, LLC
Westbury, NY  11590                             1013 Cove Road
                                                Mamaroneck, NY 10543
                                                Venture Capital Investment

BESSEC
- ------

Deer IV & Co. LLC               Delaware        General Partner
1400 Old Country Road                           Bessec Venture IV, L.P.
Suite 407                                       1400 Old Country Road
Westbury, NY  11590                             Suite 407
                                                Westbury, NY 11590
                                                Venture Capital Investment

COVE VENTURES
- -------------

Cove Road Associates, LLC       U.S.            Managing Member
1400 Old Country Road                           Cove Ventures, LLC
Suite 407                                       1013 Cove Road
Westbury, NY  11590                             Mamaroneck, NY 10543
                                                Venture Capital Investment

Robert P. Goodman               U.S.            Managing Member
1400 Old Country Road                           Cove Road Associates, LLC
Suite 407                                       1013 Cove Road
Westbury, NY  11590                             Mamaroneck, NY 10543
                                                Venture Capital Investment
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 119 of 229

                                                Present Principal Occupation,
                                                Name, Address and Principal
Name, Business Address          Citizenship     Business of Organization
- ----------------------          -----------     -----------------------------
<S>                            <C>              <C>
ADAMS CAPITAL
- -------------

Joel P. Adams                   U.S.            General Partner
518 Broad Street                                Adams Capital Management L.P.
Sewickley, PA 15143                             518 Broad Street
                                                Sewickley, PA 15143
                                                Venture Capital Investment

William C. Hulley               U.S.            General Partner
518 Broad Street                                Adams Capital Management L.P.
Sewickley, PA 15143                             518 Broad Street
                                                Sewickley, PA 15143
                                                Venture Capital Investment

Jerry S. Sullivan               U.S.            General Partner
518 Broad Street                                Adams Capital Management L.P.
Sewickley, PA 15143                             107 Ranch Road 620 S
                                                Austin, TX 78734
                                                Venture Capital Investment

William A. Frezza               U.S.            General Partner
518 Broad Street                                Adams Capital Management L.P.
Sewickley, PA 15143                             668 Stoney Hill Road
                                                Suite 155
                                                Yardley, PA 19067
                                                Venture Capital Investment

COLUMBIA INVESTORS
- ------------------

Columbia Capital, L.L.C.        Delaware        Manager
201 North Union Street                          Columbia ARTT Investors, L.L.C.
Suite 300                                       201 North Union Street
Alexandria, VA 22314                            Suite 300
                                                Alexandria, VA 22314
                                                Venture Capital Investment
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 120 of 229


                                                Present Principal Occupation,
                                                Name, Address and Principal
Name, Business Address          Citizenship     Business of Organization
- ----------------------          -----------     -----------------------------
<S>                            <C>              <C>
James B. Fleming                U.S.            President and Managing Member
201 North Union Street                          Columbia Capital, L.L.C.
Suite 300                                       201 North Union Street
Alexandria, VA 22314                            Suite 300
                                                Alexandria, VA 22314
                                                Venture Capital Investment

R. Philip Herget, III           U.S.            Senior Vice President, Treasurer and Managing
201 North Union Street                          Member
Suite 300                                       Columbia Capital, L.L.C.
Alexandria, VA 22314                            201 North Union Street
                                                Suite 300
                                                Alexandria, VA 22314
                                                Venture Capital Investment

Harry F. Hooper, III            U.S.            Senior Vice President, Secretary and Managing
201 North Union Street                          Member
Suite 300                                       Columbia Capital, L.L.C.
Alexandria, VA 22314                            201 North Union Street
                                                Suite 300
                                                Alexandria, VA 22314
                                                Venture Capital Investment

Donald A. Doering               U.S.            Chief Financial Officer, Assistant Secretary and
201 North Union Street                          Managing Member
Suite 300                                       Columbia Capital, L.L.C.
Alexandria, VA 22314                            201 North Union Street
                                                Suite 300
                                                Alexandria, VA 22314
                                                Venture Capital Investment

COLUMBIA PARTNERS
- -----------------

Columbia Capital, L.L.C.        Delaware        Manager
201 North Union Street                          Columbia ARTT Partners, L.L.C.
Suite 300                                       201 North Union Street
Alexandria, VA 22314                            Suite 300
                                                Alexandria, VA 22314
                                                Venture Capital Investment
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 121 of 229


                                                       Present Principal Occupation,
                                                       Name, Address and Principal
Name, Business Address                 Citizenship     Business of Organization
- ----------------------                 -----------     -----------------------------
<S>                                  <C>              <C>
James B. Fleming                       U.S.            President and Managing Member
201 North Union Street                                 Columbia Capital, L.L.C.
Suite 300                                              201 North Union Street
Alexandria, VA 22314                                   Suite 300
                                                       Alexandria, VA 22314
                                                       Venture Capital Investment

R. Philip Herget, III                  U.S.            Senior Vice President,
201 North Union Street                                 Treasurer and Managing Member
Suite 300                                              Columbia Capital, L.L.C.
Alexandria, VA 22314                                   201 North Union Street
                                                       Suite 300
                                                       Alexandria, VA 22314
                                                       Venture Capital Investment

Harry F. Hooper, III                   U.S.            Senior Vice President, Secretary
201 North Union Street                                 and Managing Member
Suite 300                                              Columbia Capital, L.L.C.
Alexandria, VA  22314                                  201 North Union Street
                                                       Suite 300
                                                       Alexandria, VA 22314
                                                       Venture Capital Investment

GPEII EUROPE
- ------------

Advent International Limited
Partnership                            Delaware        General Partner
75 State Street                                        Global Private
Boston, MA 02109                                       Equity II Europe
                                                       Limited Partnership
                                                       75 State Street
                                                       Boston, MA 02109
                                                       Private Equity Investment

Advent International Corporation
Partnership                            Delaware        General Partner
75 State Street                                        Advent International Limited Partnership
Boston, MA 02109                                       75 State Street
                                                       Boston, MA 02109
                                                       Private Equity Investment
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 122 of 229


                                                       Present Principal Occupation,
                                                       Name, Address and Principal
Name, Business Address                 Citizenship     Business of Organization
- ----------------------                 -----------     -----------------------------
<S>                                  <C>              <C>
OFFICERS AND DIRECTORS OF ADVENT
INTERNATIONAL CORPORATION
- ---------------------------------

Peter A. Brooke                        U.S.            Chairman
c/o Advent International Corporation                   Advent International Corporation
75 State Street                                        75 State Street
Boston, MA 02109                                       Boston, MA 02109
                                                       Private Equity Investment

Douglas R. Brown                       U.S.            Chief Executive Officer, President and Director
c/o Advent International                               Advent International Corporation
75 State Street                                        75 State Street
Boston, MA 02109                                       Boston, MA 02109
                                                       Private Equity Investment

Thomas H. Lauer                        U.S.            Senior Vice President
c/o Advent International                               Chief Financial Officer and Assistant Secretary
75 State Street                                        Advent International Corporation
Boston, MA 02109                                       75 State Street
                                                       Boston, MA 02109
                                                       Private Equity Investment

Mark Hoffman                           U.S.            Director
c/o Advent International                               Advent International Corporation
75 State Street                                        75 State Street
Boston, MA 02109                                       Boston, MA 02109
                                                       Chief Executive Officer of Hamilton Lunn Limited

Frank Savage                           U.S.            Director
c/o Advent International                               Advent International Corporation
75 State Street                                        75 State Street
Boston, MA 02109                                       Boston, MA 02109
                                                       Senior Vice President of Equitable Life Assurance
                                                       Society, Vice Chairman of Equitable Capital
                                                       Management Corp.
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 123 of 229

                                                       Present Principal Occupation,
                                                       Name, Address and Principal
Name, Business Address                 Citizenship     Business of Organization
- ----------------------                 -----------     -----------------------------
<S>                                  <C>              <C>
David W. Watson                        U.S.            Secretary
c/o Advent International                               Advent International Corporation
75 State Street                                        75 State Street
Boston, MA 02109                                       Boston, MA 02109
                                                       Attorney

GPEIIPGGM
- ---------

Advent International Limited           Delaware        General Partner
Partnership                                            Global Private
75 State Street                                        Equity II - PGGM
Boston, MA 02109                                       Limited Partnership
                                                       75 State Street
                                                       Boston, MA 02109
                                                       Private Equity Investment

OFFICERS AND DIRECTORS OF ADVENT
INTERNATIONAL CORPORATION
- --------------------------------

Advent International Corporation       Delaware        General Partner
75 State Street                                        Advent International Limited Partnership
Boston, MA 02109                                       75 State Street
                                                       Boston, MA 02109
                                                       Private Equity Investment

Peter A. Brooke                        U.S.            Chairman
c/o Advent International Corporation                   Advent International Corporation
75 State Street                                        75 State Street
Boston, MA 02109                                       Boston, MA 02109
                                                       Private Equity Investment

Douglas R. Brown                       U.S.            Chief Executive Officer, President and Director
c/o Advent International                               Advent International Corporation
75 State Street                                        75 State Street
Boston, MA 02109                                       Boston, MA 02109
                                                       Private Equity Investment
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 124 of 229

                                                       Present Principal Occupation,
                                                       Name, Address and Principal
Name, Business Address                 Citizenship     Business of Organization
- ----------------------                 -----------     -----------------------------
<S>                                  <C>              <C>
Thomas H. Lauer                        U.S.            Senior Vice President
c/o Advent International                               Chief Financial Officer and Assistant Secretary
75 State Street                                        Advent International Corporation
Boston, MA 02109                                       75 State Street
                                                       Boston, MA 02109
                                                       Private Equity Investment

Mark Hoffman                           U.S.            Director
c/o Advent International                               Advent International Corporation
75 State Street                                        75 State Street
Boston, MA 02109                                       Boston, MA 02109
                                                       Chief Executive Officer of Hamilton Lunn Limited

Frank Savage                           U.S.            Director
c/o Advent International                               Advent International Corporation
75 State Street                                        75 State Street
Boston, MA 02109                                       Boston, MA 02109
                                                       Senior Vice President of Equitable Life Assurance
                                                       Society, Vice Chairman of Equitable Capital
                                                       Management Corp.

David W. Watson                        U.S.            Secretary
c/o Advent International                               Advent International Corporation
75 State Street                                        75 State Street
Boston, MA 02109                                       Boston, MA 02109
                                                       Attorney

DIGITAL
- -------

Advent International Limited           Delaware        General Partner
Partnership                                            Digital Media & Communications
75 State Street                                        Limited Partnership
Boston, MA 02109                                       75 State Street
                                                       Boston, MA 02109
                                                       Private Equity Investment
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 125 of 229

                                                       Present Principal Occupation,
                                                       Name, Address and Principal
Name, Business Address                 Citizenship     Business of Organization
- ----------------------                 -----------     -----------------------------
<S>                                  <C>              <C>
Advent International Corporation       Delaware        General Partner
75 State Street                                        Advent International Limited Partnership
Boston, MA 02109                                       75 State Street
                                                       Boston, MA 02109
                                                       Private Equity Investment

OFFICERS AND DIRECTORS OF ADVENT
INTERNATIONAL CORPORATION
- --------------------------------

Peter A. Brooke                        U.S.            Chairman
c/o Advent International Corporation                   Advent International Corporation
75 State Street                                        75 State Street
Boston, MA 02109                                       Boston, MA 02109
                                                       Private Equity Investment

Douglas R. Brown                       U.S.            Chief Executive Officer, President and Director
c/o Advent International                               Advent International Corporation
75 State Street                                        75 State Street
Boston, MA 02109                                       Boston, MA 02109
                                                       Private Equity Investment

Thomas H. Lauer                        U.S.            Senior Vice President
c/o Advent International                               Chief Financial Officer and Assistant Secretary
75 State Street                                        Advent International Corporation
Boston, MA 02109                                       75 State Street
                                                       Boston, MA 02109
                                                       Private Equity Investment

Mark Hoffman                           U.S.            Director
c/o Advent International                               Advent International Corporation
75 State Street                                        75 State Street
Boston, MA 02109                                       Boston, MA 02109
                                                       Chief Executive Officer of Hamilton Lunn Limited
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 126 of 229

                                                           Present Principal Occupation,
                                                           Name, Address and Principal
Name, Business Address                     Citizenship     Business of Organization
- ----------------------                     -----------     -----------------------------
<S>                                        <C>              <C>
Frank Savage                               U.S.            Director
c/o Advent International                                   Advent International Corporation
75 State Street                                            75 State Street
Boston, MA 02109                                           Boston, MA 02109
                                                           Senior Vice President of Equitable Life Assurance
                                                           Society, Vice Chairman of Equitable Capital
                                                           Management Corp.

David W. Watson                            U.S.            Secretary
c/o Advent International                                   Advent International Corporation
75 State Street                                            75 State Street
Boston, MA 02109                                           Boston, MA 02109
                                                           Attorney

OAKSTONE
- --------

Advent International Limited Partnership   Delaware        General Partner
75 State Street                                            Oakstone Ventures
Boston, MA 02109                                           Limited Partnership
                                                           75 State Street
                                                           Boston, MA 02109
                                                           Private Equity Investment

Advent International Corporation           Delaware        General Partner
75 State Street                                            Advent International Limited Partnership
Boston, MA 02109                                           75 State Street
                                                           Boston, MA 02109
                                                           Private Equity Investment

OFFICERS AND DIRECTORS OF ADVENT
INTERNATIONAL CORPORATION
- --------------------------------

Peter A. Brooke                            U.S.            Chairman
c/o Advent International Corporation                       Advent International Corporation
75 State Street                                            75 State Street
Boston, MA 02109                                           Boston, MA 02109
                                                           Private Equity Investment
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 127 of 229

                                                         Present Principal Occupation,
                                                         Name, Address and Principal
Name, Business Address                   Citizenship     Business of Organization
- ----------------------                   -----------     -----------------------------
<S>                                     <C>              <C>
Douglas R. Brown                         U.S.            Chief Executive Officer, President and Director
c/o Advent International                                 Advent International Corporation
75 State Street                                          75 State Street
Boston, MA 02109                                         Boston, MA 02109
                                                         Private Equity Investment

Thomas H. Lauer                          U.S.            Senior Vice President
c/o Advent International                                 Chief Financial Officer and Assistant Secretary
75 State Street                                          Advent International Corporation
Boston, MA 02109                                         75 State Street
                                                         Boston, MA 02109
                                                         Private Equity Investment

Mark Hoffman                             U.S.            Director
c/o Advent International                                 Advent International Corporation
75 State Street                                          75 State Street
Boston, MA 02109                                         Boston, MA 02109
                                                         Chief Executive Officer of Hamilton Lunn Limited

Frank Savage                             U.S.            Director
c/o Advent International                                 Advent International Corporation
75 State Street                                          75 State Street
Boston, MA 02109                                         Boston, MA 02109
                                                         Senior Vice President of Equitable Life Assurance
                                                         Society, Vice Chairman of Equitable Capital
                                                         Management Corp.

David W. Watson                          U.S.            Secretary
c/o Advent International                                 Advent International Corporation
75 State Street                                          75 State Street
Boston, MA 02109                                         Boston, MA 02109
                                                         Attorney
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 128 of 229

                                                             Present Principal Occupation,
                                                             Name, Address and Principal
Name, Business Address                       Citizenship     Business of Organization
- ----------------------                       -----------     -----------------------------
<S>                                         <C>              <C>
ADVENT CROWN
- ------------

Advent International Limited                 Delaware        General Partner
Partnership                                                  Advent Crown Fund II C.V.
75 State Street                                              75 State Street
Boston, MA 02109                                             Boston, MA 02109
                                                             Private Equity Investment

Advent International Corporation             Delaware        General Partner
75 State Street                                              Advent International Limited Partnership
Boston, MA 02109                                             75 State Street
                                                             Boston, MA 02109
                                                             Private Equity Investment

OFFICERS AND DIRECTORS OF ADVENT
INTERNATIONAL CORPORATION
- --------------------------------

Peter A. Brooke                              U.S.            Chairman
c/o Advent International Corporation                         Advent International Corporation
75 State Street                                              75 State Street
Boston, MA 02109                                             Boston, MA 02109
                                                             Private Equity Investment

Douglas R. Brown                             U.S.            Chief Executive Officer,
c/o Advent International                                     President and Director
75 State Street                                              Advent International Corporation
Boston, MA 02109                                             75 State Street
                                                             Boston, MA 02109
                                                             Private Equity Investment

Thomas H. Lauer                              U.S.            Senior Vice President
c/o Advent International                                     Chief Financial Officer and Assistant Secretary
75 State Street                                              Advent International Corporation
Boston, MA 02109                                             75 State Street
                                                             Boston, MA 02109
                                                             Private Equity Investment
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 129 of 229

                                                             Present Principal Occupation,
                                                             Name, Address and Principal
Name, Business Address                       Citizenship     Business of Organization
- ----------------------                       -----------     -----------------------------
<S>                                         <C>              <C>
Mark Hoffman                                 U.S.            Director
c/o Advent International                                     Advent International Corporation
75 State Street                                              75 State Street
Boston, MA 02109                                             Boston, MA 02109
                                                             Chief Executive Officer of Hamilton Lunn Limited

Frank Savage                                 U.S.            Director
c/o Advent International                                     Advent International Corporation
75 State Street                                              75 State Street
Boston, MA 02109                                             Boston, MA 02109
                                                             Senior Vice President of Equitable Life Assurance
                                                             Society, Vice Chairman of Equitable Capital
                                                             Management Corp.

David W. Watson                              U.S.            Secretary
c/o Advent International                                     Advent International Corporation
Limited Partnership                                          75 State Street
75 State Street                                              Boston, MA 02109
Boston, MA 02109                                             Attorney

ADWEST
- ------

Advent International Limited                 Delaware        General Partner
Partnership                                                  Adwest
75 State Street                                              Limited Partnership
Boston, MA 02109                                             75 State Street
                                                             Boston, MA 02109
                                                             Private Equity Investment

Advent International Corporation             Delaware        General Partner
75 State Street                                              Advent International Limited Partnership
Boston, MA 02109                                             75 State Street
                                                             Boston, MA 02109
                                                             Private Equity Investment
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 130 of 229

                                                             Present Principal Occupation,
                                                             Name, Address and Principal
Name, Business Address                       Citizenship     Business of Organization
- ----------------------                       -----------     -----------------------------
<S>                                         <C>              <C>
OFFICERS AND DIRECTORS OF ADVENT
INTERNATIONAL CORPORATION
- --------------------------------

Peter A. Brooke                              U.S.            Chairman
c/o Advent International Corporation                         Advent International Corporation
75 State Street                                              75 State Street
Boston, MA 02109                                             Boston, MA 02109
                                                             Private Equity Investment

Douglas R. Brown                             U.S.            Chief Executive Officer, President and Director
c/o Advent International                                     Advent International Corporation
75 State Street                                              75 State Street
Boston, MA 02109                                             Boston, MA 02109
                                                             Private Equity Investment

Thomas H. Lauer                              U.S.            Senior Vice President
c/o Advent International                                     Chief Financial Officer and Assistant Secretary
75 State Street                                              Advent International Corporation
Boston, MA 02109                                             75 State Street
                                                             Boston, MA 02109
                                                             Private Equity Investment

Mark Hoffman                                 U.S.            Director
c/o Advent International                                     Advent International Corporation
75 State Street                                              75 State Street
Boston, MA 02109                                             Boston, MA 02109
                                                             Chief Executive Officer of Hamilton Lunn Limited

Frank Savage                                 U.S.            Director
c/o Advent International                                     Advent International Corporation
75 State Street                                              75 State Street
Boston, MA 02109                                             Boston, MA 02109
                                                             Senior Vice President of Equitable Life Assurance
                                                             Society, Vice Chairman of Equitable Capital
                                                             Management Corp.
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 131 of 229

                                                        Present Principal Occupation,
                                                        Name, Address and Principal
Name, Business Address                  Citizenship     Business of Organization
- ----------------------                  -----------     -----------------------------
<S>                                         <C>              <C>
David W. Watson                         U.S.            Secretary
c/o Advent International                                Advent International Corporation
75 State Street                                         75 State Street
Boston, MA 02109                                        Boston, MA 02109
                                                        Attorney

ADVENT GLOBAL
- -------------

Advent Global                           Delaware        General Partner
Management Limited Partnership                          Advent Global
75 State Street                                         GECC Limited Partnership
Boston, MA 02109                                        75 State Street
                                                        Boston, MA 02109
                                                        Private Equity Investment

Advent International Limited            Delaware        General Partner
Partnership                                             Advent Global Management
75 State Street                                         Limited Partnership
Boston, MA 02109                                        75 State Street
                                                        Boston, MA 02109
                                                        Private Equity Investment

Advent International Corporation        Delaware        General Partner
75 State Street                                         Advent International Limited Partnership
Boston, MA 02109                                        75 State Street
                                                        Boston, MA 02109
                                                        Private Equity Investment

OFFICERS AND DIRECTORS OF ADVENT
INTERNATIONAL CORPORATION
- --------------------------------

Peter A. Brooke                         U.S.            Chairman
c/o Advent International Corporation                    Advent International Corporation
75 State Street                                         75 State Street
Boston, MA 02109                                        Boston, MA 02109
                                                        Private Equity Investment
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 132 of 229

                                                        Present Principal Occupation,
                                                        Name, Address and Principal
Name, Business Address                  Citizenship     Business of Organization
- ----------------------                  -----------     -----------------------------
<S>                                    <C>              <C>
Douglas R. Brown                        U.S.            Chief Executive Officer, President and Director
c/o Advent International Limited                        Advent International Corporation
Partnership                                             75 State Street
75 State Street                                         Boston, MA 02109
Boston, MA 02109                                        Private Equity Investment

Thomas H. Lauer                         U.S.            Senior Vice President
c/o Advent International Limited                        Chief Financial Officer and Assistant Secretary
Partnership                                             Advent International Corporation
75 State Street                                         75 State Street
Boston, MA 02109                                        Boston, MA 02109
                                                        Private Equity Investment

Mark Hoffman                            U.S.            Director
c/o Advent International                                Advent International Corporation
75 State Street                                         75 State Street
Boston, MA 02109                                        Boston, MA 02109
                                                        Chief Executive Officer of Hamilton Lunn Limited

Frank Savage                            U.S.            Director
c/o Advent International                                Advent International Corporation
75 State Street                                         75 State Street
Boston, MA 02109                                        Boston, MA 02109
                                                        Senior Vice President of Equitable Life Assurance
                                                        Society, Vice Chairman of Equitable Capital
                                                        Management Corp.

David W. Watson                         U.S.            Secretary
c/o Advent International                                Advent International Corporation
75 State Street                                         75 State Street
Boston, MA 02109                                        Boston, MA 02109
                                                        Private Equity Investment
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 133 of 229

                                                        Present Principal Occupation,
                                                        Name, Address and Principal
Name, Business Address                  Citizenship     Business of Organization
- ----------------------                  -----------     -----------------------------
<S>                                    <C>              <C>
ADVENT PARTNERS
- ---------------

Advent International Corporation        Delaware        General Partner
75 State Street                                         Advent Partners Limited Partnership
Boston, MA 02109                                        75 State Street
                                                        Boston, MA 02109
                                                        Attorney

OFFICERS AND DIRECTORS OF ADVENT
INTERNATIONAL CORPORATION
- --------------------------------

Peter A. Brooke                         U.S.            Chairman
c/o Advent International Corporation                    Advent International Corporation
75 State Street                                         75 State Street
Boston, MA 02109                                        Boston, MA 02109
                                                        Private Equity Investment

Douglas R. Brown                        U.S.            Chief Executive Officer, President and Director
c/o Advent International                                Advent International Corporation
75 State Street                                         75 State Street
Boston, MA 02109                                        Boston, MA 02109
                                                        Private Equity Investment

Thomas H. Lauer                         U.S.            Senior Vice President
c/o Advent International                                Chief Financial Officer and Assistant Secretary
75 State Street                                         Advent International Corporation
Boston, MA 02109                                        75 State Street
                                                        Boston, MA 02109
                                                        Private Equity Investment

Mark Hoffman                            U.S.            Director
c/o Advent International                                Advent International Corporation
75 State Street                                         75 State Street
Boston, MA 02109                                        Boston, MA 02109
                                                        Chief Executive Officer of Hamilton
                                                        Lunn Limited
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 134 of 229

                                                         Present Principal Occupation,
                                                         Name, Address and Principal
Name, Business Address                   Citizenship     Business of Organization
- ----------------------                   -----------     -----------------------------
<S>                                    <C>              <C>
Frank Savage                             U.S.            Director
c/o Advent International                                 Advent International Corporation
75 State Street                                          75 State Street
Boston, MA 02109                                         Boston, MA 02109
                                                         Senior Vice President of Equitable Life Assurance
                                                         Society, Vice Chairman of Equitable Capital
                                                         Management Corp.

David W. Watson                          U.S.            Secretary
c/o Advent International                                 Advent International Corporation
75 State Street                                          75 State Street
Boston, MA 02109                                         Boston, MA 02109
                                                         Attorney

USTI
- ----

Joseph P. Nacchio                        U.S.            Director
555 17th Street                                          U.S. Telesource, Inc.
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

Drake S. Tempest                         U.S.            Executive Vice President, General
555 17th Street                                          Counsel and Secretary
Denver, CO  80202                                        U.S. Telesource, Inc.
                                                         555 17th Street
                                                         Denver, CO 80202

Robert S. Woodruff                       U.S.            Executive Vice President, Chief Financial Officer
555 17th Street                                          and Director
Denver, CO  80202                                        U.S. Telesource, Inc.
                                                         555 17th Street
                                                         Denver, CO 80202

Marc B. Weisberg                         U.S.            President, Chief Executive Officer and Director
555 17th Street                                          U.S. Telesource, Inc.
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 135 of 229

                                                         Present Principal Occupation,
                                                         Name, Address and Principal
Name, Business Address                   Citizenship     Business of Organization
- ----------------------                   -----------     -----------------------------
<S>                                    <C>              <C>
Stephen H. Shoemaker                     U.S.            Vice President and Treasurer
555 17th Street                                          U.S. Telesource, Inc.
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

Yash A. Rana                             Indian          Assistant Secretary
555 17th Street                                          U.S. Telesource, Inc.
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

Jeff VonDeylen                           U.S.            Vice President and Controller
555 17th Street                                          U.S. Telesource, Inc.
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

Kelly S. Carter                          U.S.            Assistant Treasurer
555 17th Street                                          U.S. Telesource, Inc.
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

QCC
- ---

OFFICERS AND DIRECTORS

Joseph P. Nacchio                        U.S.            Chairman and Chief Executive
555 17th Street                                          Officer and Director
Denver, CO  80202                                        Qwest Communications Corporation
                                                         555 17th Street
                                                         Denver, CO 80202
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 136 of 229

                                                         Present Principal Occupation,
                                                         Name, Address and Principal
Name, Business Address                   Citizenship     Business of Organization
- ----------------------                   -----------     -----------------------------
<S>                                    <C>              <C>
Craig D. Slater                          U.S.            Director
555 17th Street                                          Qwest Communications Corporation
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

Drake S. Tempest                         U.S.            Executive Vice President, General
555 17th Street                                          Counsel, Secretary and Director
Denver, CO  80202                                        Qwest Communications Corporation
                                                         555 17th Street
                                                         Denver, CO 80202

Robert S. Woodruff                       U.S.            Director, Executive Vice President -
555 17th Street                                          Finance and Chief Financial Officer
Denver, CO  80202                                        Qwest Communications Corporation
                                                         555 17th Street
                                                         Denver, CO 80202

Afshin Mohebbi                           U.S.            President and Chief Operating
555 17th Street                                          Officer
Denver, CO  80202                                        Qwest Communications Corporation
                                                         555 17th Street
                                                         Denver, CO 80202

Marc B. Weisberg                         U.S.            Senior Vice President - Corporate
555 17th Street                                          Development
Denver, CO  80202                                        Qwest Communications Corporation
                                                         555 17th Street
                                                         Denver, CO 80202

Stephen H. Shoemaker                     U.S.            Treasurer
555 17th Street                                          Qwest Communications Corporation
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

Yash A. Rana                             Indian          Assistant Secretary
555 17th Street                                          Qwest Communications Corporation
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 137 of 229

                                                         Present Principal Occupation,
                                                         Name, Address and Principal
Name, Business Address                   Citizenship     Business of Organization
- ----------------------                   -----------     -----------------------------
<S>                                    <C>              <C>

Craig D. Slater                          U.S.            Director Qwest Communications Corporation
555 17th Street                                          555 17th Street
Denver, CO  80202                                        Denver, CO 80202

QC
- --

OFFICERS AND DIRECTORS

Joseph P. Nacchio                        U.S.            President, Chief Executive
555 17th Street                                          Officer and Director
Denver, CO  80202                                        Qwest Corporation
                                                         555 17th Street
                                                         Denver, CO 80202
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 138 of 229

                                                         Present Principal Occupation,
                                                         Name, Address and Principal
Name, Business Address                   Citizenship     Business of Organization
- ----------------------                   -----------     -----------------------------
<S>                                    <C>              <C>
Craig D. Slater                          U.S.            Director
555 17th Street                                          Qwest Corporation
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

Robert S. Woodruff                       U.S.            Director
555 17th Street                                          Qwest Corporation
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

Drake S. Tempest                         U.S.            Executive Vice President, General Counsel
555 17th Street                                          Secretary and Director
Denver, CO  80202                                        Qwest Corporation
                                                         555 17th Street
                                                         Denver, CO 80202

Marc B. Weisberg                         U.S.            Senior Vice Presiden, Corporate Development
555 17th Street                                          Qwest Corporation
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

Stephen H. Shoemaker                     U.S.            Vice President and Treasurer
555 17th Street                                          Qwest Corporation
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

Yash A. Rana                             Indian          Assistant Secretary
555 17th Street                                          Qwest Corporation
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

Kelly S. Carter                          U.S.            Assistant Treasurer
555 17th Street                                          Qwest Corporation
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

Jeff VonDeylen                           U.S.            Vice President and Controller
555 17th Street                                          Qwest Corporation
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 139 of 229

QCI
- ---

OFFICERS AND DIRECTORS
<S>                                    <C>              <C>
Philip F. Anschutz                       U.S.            Director and Chairman of the Board
555 17th Street                                          Qwest Communications International Inc.
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

Joseph P. Nacchio                        U.S.            Director, Chairman and Chief
555 17th Street                                          Executive Officer
Denver, CO  80202                                        Qwest Communications International Inc.
                                                         555 17th Street
                                                         Denver, CO 80202

Jordan L. Haines                         U.S.            Director
555 17th Street                                          Qwest Communications International Inc.
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO  80202

Jerry Davis                              U.S.            Director
555 17th Street                                          Qwest Communications International Inc.
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

Cannon Y. Harvey                         U.S.            Director
555 17th Street                                          Qwest Communications International Inc.
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

Douglas M. Karp                          U.S.            Director Qwest Communications International Inc.
555 17th Street                                          555 17th Street
Denver, CO  80202                                        Denver, CO 80202

Vinod Khosla                             U.S.            Director
555 17th Street                                          Qwest Communications International Inc.
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

Richard T. Liebhaber                     U.S.            Director
555 17th Street                                          Qwest Communications International Inc.
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

Douglas L. Polson                        U.S.            Director Qwest Communications International Inc.
555 17th Street                                          555 17th Street
Denver, CO  80202                                        Denver, CO 80202

Craig D. Slater                          U.S.            Director
555 17th Street                                          Qwest Communications International Inc.
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

W. Thomas Stephens                       U.S.            Director Qwest Communications International Inc.
555 17th Street                                          555 17th Street
Denver, CO  80202                                        Denver, CO 80202
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 140 of 229

                                                         Present Principal Occupation,
                                                         Name, Address and Principal
Name, Business Address                   Citizenship     Business of Organization
- ----------------------                   -----------     -----------------------------
<S>                                    <C>              <C>
Robert S. Woodruff                       U.S.            Executive Vice President - Finance,
555 17th Street                                          Chief Financial Officer and Director
Denver, CO  80202                                        Qwest Communications International Inc.
                                                         555 17th Street
                                                         Denver, CO 80202

Drake S. Tempest                         U.S.            Executive Vice President and
555 17th Street                                          General Counsel and Secretary
Denver, CO  80202                                        Qwest Communications International Inc.
                                                         555 17th Street
                                                         Denver, CO 80202

Stephen H. Shoemaker                     U.S.            Vice President and Treasurer
555 17th Street                                          Qwest Communications International Inc.
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

Yash A. Rana                             Indian          Assistant Secretary
555 17th Street                                          Qwest Communications International Inc.
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 141 of 229

                                                         Present Principal Occupation,
                                                         Name, Address and Principal
Name, Business Address                   Citizenship     Business of Organization
- ----------------------                   -----------     -----------------------------
<S>                                    <C>              <C>
AC
- --

OFFICERS AND DIRECTORS

Philip F. Anschutz                       U.S.            Chairman, Chief Executive Officer and Director
555 17th Street                                          Anschutz Company
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

Cannon Y. Harvey                         U.S.            President, Chief Operating Officer and Director
555 17th Street                                          Anschutz Company
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

Douglas L. Polson                        U.S.            Vice President - Finance, Assistant Secretary and Director
555 17th Street                                          Anschutz Company
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

Miles A. Williams                        U.S.            Executive Vice President and Director
555 17th Street                                          Anschutz Company
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

Richard M. Jones                         U.S.            Vice President, General Counsel and Assistant
555 17th Street                                          Secretary
Denver, CO  80202                                        Anschutz Company
                                                         555 17th Street
                                                         Denver, CO 80202

Craig D. Slater                          U.S.            Executive Vice President and Director
555 17th Street                                          Anschutz Company
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

Lynn T. Wood                             U.S.            Secretary
555 17th Street                                          Anschutz Company
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
                                                                 Page 142 of 229

                                                         Present Principal Occupation,
                                                         Name, Address and Principal
Name, Business Address                   Citizenship     Business of Organization
- ----------------------                   -----------     -----------------------------
<S>                                    <C>              <C>
Thomas G. Kundert                        U.S.            Treasurer and Assistant Secretary
555 17th Street                                          Anschutz Company
Denver, CO  80202                                        555 17th Street
                                                         Denver, CO 80202

</TABLE>


                                                                 Page 143 of 229


                                    EXHIBIT C

- --------------------------------------------------------------------------------





                       PREFERRED STOCK PURCHASE AGREEMENT

                                  by and among

                          ADVANCED RADIO TELECOM CORP.

                                       and

                   THE PURCHASERS LISTED ON SCHEDULE I HERETO






                            Dated as of June 1, 1999





- --------------------------------------------------------------------------------
<PAGE>
                                                                 Page 144 of 229

                       PREFERRED STOCK PURCHASE AGREEMENT

         This Preferred Stock Purchase Agreement is dated as of June 1, 1999
(this "AGREEMENT"), among Advanced Radio Telecom Corp., a Delaware corporation
(the "COMPANY"), and the purchasers listed on Schedule I hereto (the
"PURCHASERS").

                                   WITNESSETH:

         WHEREAS, the Purchasers wish to purchase from the Company, and the
Company wishes to sell and issue to the Purchasers (the "STOCK PURCHASE"), an
aggregate of 2,635,908 shares of the Company's Series A Convertible Preferred
Stock, $0.001 par value per share (the "SERIES A PREFERRED STOCK") and 501,592
shares of the Company's Series B Non-Voting Convertible Preferred Stock, $0.001
par value per share (the "SERIES B PREFERRED STOCK", and together with the
Series A Preferred Stock and the Series C Non-Voting Convertible Preferred
Stock, $0.001 par value per share (the "SERIES C PREFERRED STOCK"), the
"PREFERRED STOCK"); and

         WHEREAS, contemporaneously with the execution of this Agreement, the
Purchasers and the Company are executing and delivering the Standstill Agreement
(hereinafter defined) and the Company is executing and delivering the Warrants
(hereinafter defined) and the Notes (hereinafter defined) and the Purchasers are
advancing the Company $45,019,920; and

         WHEREAS, the Purchasers and the Company are entering into this
Agreement to provide for the purchase and sale of the Preferred Stock and to
establish various rights and obligations in connection therewith.

         NOW, THEREFORE, in consideration of the premises and the mutual
covenants herein set forth, the parties agree as follows:

                                   ARTICLE I.

                                  THE PURCHASE

         Section 1.1 DEFINITIONS. Certain terms are used in this Agreement as
specifically defined herein. These definitions are set forth herein or referred
to in Section 7.4 hereof.

         Section 1.2 SALE AND PURCHASE OF PREFERRED STOCK.

              SECTION 1.2.1. PURCHASE. Subject to the terms and conditions of
this Agreement, and in reliance on the representations and warranties set forth
in this Agreement, the Company hereby agrees to sell to each of the Purchasers,
and each of the Purchasers hereby agrees severally to purchase from the Company,
at the Closing (as hereinafter defined) and at a purchase price of $80.00 per
share (the "PURCHASE PRICE"), the number of shares of Series A

<PAGE>
                                                                 Page 145 of 229

Preferred Stock and the number of shares of Series B Preferred Stock as are set
forth on Schedule I as being purchased by such Purchaser (such shares of Series
A Preferred Stock and Series B Preferred Stock purchased hereunder, the
"SHARES"). The aggregate Purchase Price of the Shares purchased and sold
hereunder is $251,000,000 (the "INVESTMENT"). The terms of the Series A
Preferred Stock, the Series B Preferred Stock and the Series C Preferred Stock
shall be those set forth in the Certificate of Designation (as hereinafter
defined).

              SECTION 1.2.2. ALTERNATIVE COMMITMENT. In the event that MeriTech
Capital Partners ("MeriTech") has not made the advance provided in Section 1.3
prior to June 15, 1999, Oak Investment Partners ("Oak"), Worldview Technology
("Worldview"), Accel Partners ("Accel") and Brentwood Venture Capital
("Brentwood") severally agree to purchase from the Company at the Closing at a
purchase price of $80.00 per share the additional number of shares of Series A
Preferred Stock and the additional number of shares of Series B Preferred Stock
as are set forth on Schedule I, and MeriTech on June 15, 1999 shall cease to be
a party to this Agreement for all purposes.

         Section 1.3 BRIDGE LOAN AND WARRANTS. The Purchasers severally agree to
advance to the Company an aggregate of $50,000,000 (the "LOAN") on the terms set
forth below. On the date of this Agreement, each of the Purchasers other than
MeriTech agrees to advance to the Company the amount set forth opposite its
respective name on Schedule I, and prior to June 15, 1999, MeriTech agrees to
advance to the Company the amount set forth opposite its name on Schedule I.
MeriTech shall provide the Company two business days notice of the date on which
it shall make the advance. If MeriTech has not made the advance by June 15,
1999, on that date Oak, Worldview, Accel and Brentwood severally agree to
advance to the Company the additional amount set forth opposite its respective
name on Schedule I. Each advance of the Loan shall be made by wire transfer of
immediately available funds to the account of the Company specified in Schedule
II hereto. The Company's obligations to pay the Loan shall be evidenced by the
Company's notes in substantially the form of EXHIBIT A (each a "NOTE", and
collectively the "NOTES"). The Notes shall bear interest at a rate of 11% per
annum, which interest shall accrue daily but not compound. Principal under each
Note will be due and payable on the earlier to occur of (i) the Closing
hereunder and (ii) the date which is 150 days from the date of this Agreement,
or such later date mutually agreed to by the Company and Two-Thirds in Interest
(as hereinafter defined) of the Purchasers (the "FINAL MATURITY DATE"). Such
Final Maturity Date may be accelerated as provided in the Notes.

              SECTION 1.3.1. PREPAYMENT. Interest shall be due and payable on
any prepayment of the Note, either in cash or, if at Closing at the Company's
option, in shares of the Company's Series A Preferred Stock (valued at $80.00
per share).

              SECTION 1.3.2. APPLICATION OF NOTE PROCEEDS TO PURCHASE PRICE. At
the Closing, each Purchaser shall return its outstanding Note to the Company,
and the Company shall cancel each Note and shall apply all amounts outstanding
under each Note, together with all accrued and unpaid interest thereon, to the
Purchase Price payable by the respective Purchaser.

<PAGE>
                                                                 Page 146 of 229

If either the Company or a Purchaser so elects, at the Closing the Company shall
pay the accrued and unpaid interest payable on such Purchaser's Note in cash.

              SECTION 1.3.3. WARRANTS. On the date of this Agreement, upon its
receipt of the Loan, the Company will issue to each of the Purchasers that has
advanced its portion of the Loan a warrant (each a "WARRANT", and collectively,
the "WARRANTS") to purchase the number of shares of Common Stock set forth
opposite such Purchaser's name on Schedule I, in substantially the form of
EXHIBIT G. On the date on which MeriTech advances to the Company its portion of
the Loan, the Company will issue to MeriTech a Warrant to purchase the number of
shares of Common Stock set forth opposite its name on Schedule I or on June 15,
1999, if Oak, Worldview, Accel and Brentwood shall make the additional advances
on the Loan in lieu of MeriTech pursuant to Section 1.3, upon receipt of those
advances the Company will issue to each of Oak, Worldview, Accel and Brentwood
Warrants to purchase the additional number of shares of Common Stock set forth
opposite its respective name on Schedule I under the designation "MeriTech
Warrants."

         Section 1.4 THE CLOSING. Unless this Agreement shall have been
terminated pursuant to Section 6.1, and subject to the satisfaction or waiver of
the conditions set forth in Article V, the consummation of the transactions
contemplated hereby (the "CLOSING") will take place as promptly as practicable
(and in any event within two business days) after satisfaction or waiver of the
conditions set forth in Article V (the "CLOSING DATE"), at the offices of Ropes
& Gray, 885 Third Avenue, New York, New York, unless another date, time or place
is agreed to in writing by the Company and Two-Thirds in Interest of the
Purchasers. At the Closing and subject to the conditions provided herein, the
Company will deliver to each Purchaser a certificate, registered in such
Purchaser's name, representing the number of Shares to be purchased by such
Purchaser hereunder against payment of the aggregate purchase price therefor by
cancellation of the Notes as described in Section 1.3 and by wire transfer of
the remaining amount in immediately available funds to the Company's account as
set forth on Schedule II hereto.


                                  ARTICLE II.

                  REPRESENTATIONS AND WARRANTIES OF THE COMPANY

         Subject to Section 7.1 hereof, the Company hereby represents and
warrants to the Purchasers that, except as set forth in the written disclosure
schedule delivered simultaneously with the execution and delivery of this
Agreement (the "COMPANY DISCLOSURE SCHEDULE"):

         Section 2.1 ORGANIZATION AND QUALIFICATION; SUBSIDIARIES. The Company
is a corporation duly organized, validly existing and in good standing under the
laws of the State of Delaware. Except as set forth in Schedule 2.1, each of the
Company's subsidiaries is a corporation duly organized, validly existing and in
good standing under the laws of the jurisdiction of its incorporation. Except as
set forth in Schedule 2.1, each of the Company and each of its subsidiaries has
the requisite corporate power and authority to own, lease, license, use

<PAGE>
                                                                 Page 147 of 229

or operate the properties it purports to own, operate, license, use or lease and
to carry on its business as it is now being conducted and proposed to be
conducted. Each of the Company and each of its subsidiaries is duly qualified or
licensed as a foreign corporation to do business, and is in good standing, in
each jurisdiction where the character of its properties owned, leased or
operated by it or the nature of its activities makes such qualification or
licensing necessary, except for such failures to be so duly qualified or
licensed and in good standing that do not constitute a Material Adverse Effect.

         Section 2.2 CERTIFICATE OF INCORPORATION AND BY-LAWS. The Company has
heretofore made available to the Purchasers a complete and correct copy of its
Certificate of Incorporation and By-Laws as most recently restated and
subsequently amended to date. Except as set forth in Schedule 2.2, such
Certificate of Incorporation and By-Laws, and the certificate of incorporation
and by-laws (or equivalent organizational documents) of each of the Company's
subsidiaries (the "COMPANY SUBSIDIARY DOCUMENTS"), are in full force and effect.
Neither the Company nor any of its subsidiaries is in violation of any of the
provisions of its Certificate of Incorporation or By-Laws or Company Subsidiary
Documents, except for such violations as do not constitute a Material Adverse
Effect.

         Section 2.3       CAPITALIZATION.

              (a) The authorized capital stock of the Company consists of (i)
         100,000,000 shares of common stock, $0.001 par value per share ("COMMON
         STOCK") and (ii) 10,000,000 shares of preferred stock, $0.001 par value
         per share. As of May 10, 1999, (i)(A) 1,000,000 shares of preferred
         stock were designated as series of Junior Preferred Stock, none of
         which were issued and outstanding, and (B) 27,200,699 shares of Common
         Stock were issued and outstanding, all of which are duly authorized,
         validly issued, fully paid and nonassessable, and no shares were held
         in treasury, (ii) 8,051,551 shares of Common Stock were reserved for
         future issuance pursuant to stock options ("STOCK OPTIONS") or other
         equity incentives granted or to be granted under the Company's Restated
         Equity Incentive Plan, as amended by the Company's Board of Directors
         (the "BOARD") subject to stockholder approval, the Company's 1996
         Non-Employee Directors Automatic Stock Option Plan or the Company's
         1997 Equity Incentive Plan for Non-Employee Directors (collectively,
         the "COMPANY STOCK OPTION PLANS"), (iv) 2,178,490 shares of Common
         Stock were reserved for future issuance upon the exercise of certain
         warrants set forth on SCHEDULE 2.3, and (v) shares of Common Stock were
         reserved for future issuance from time to time as required pursuant to
         the Company's 401(k) Plan.

              (b) On or prior to the Closing Date, the Certificate of
         Designation (as hereinafter defined) will have been duly adopted and
         filed with the Secretary of State of Delaware and, on the Closing Date,
         shall be in full force and effect. On or prior to the Closing Date, the
         Company shall reserve for issuance the number of shares of Common Stock
         issuable upon the conversion of the Shares issued to the Purchasers
         pursuant to this Agreement. All shares of Common Stock issuable
         pursuant to the preceding sentence,

<PAGE>
                                                                 Page 148 of 229

         upon issuance on the terms and conditions specified in the instruments
         pursuant to which they are issuable, will be duly authorized, validly
         issued, fully paid and non assessable. The Shares issued on the Closing
         Date will, upon payment of the Purchase Price therefor, be duly
         authorized, validly issued, fully paid and nonassessable.

              (c) As of the date hereof, except as set forth in SCHEDULE 2.3 or
         the Company SEC Reports, there are no options, warrants or other
         rights, agreements, arrangements or commitments of any character
         relating to the issued or unissued capital stock of the Company or any
         of its subsidiaries or obligating the Company or any of its
         subsidiaries to issue or sell any shares of capital stock of, or other
         equity interests in, the Company or any of its subsidiaries. All shares
         of Common Stock subject to issuance thereunder, upon issuance on the
         terms and conditions specified in the instruments pursuant to which
         they are issuable, will be duly authorized, validly issued, fully paid
         and non-assessable. Except as set forth in Schedule 2.3, there are no
         obligations, contingent or otherwise, of the Company or any of its
         subsidiaries to repurchase, redeem or otherwise acquire any shares of
         capital stock or the capital stock of any subsidiary or to provide
         funds to or make any investment (in the form of a loan, capital
         contribution or otherwise) in any such subsidiary or any other entity
         other than guarantees of obligations of subsidiaries entered into in
         the ordinary course of business and except for the terms of the Company
         Stock Option Plans. Except as set forth in Schedule 2.3, all of the
         outstanding shares of capital stock of each of the Company's
         subsidiaries are duly authorized, validly issued, fully paid and
         nonassessable, and all such shares are beneficially owned by the
         Company or another subsidiary of the Company, free and clear of all
         security interests, liens, claims, pledges, agreements, limitations in
         the Company's voting rights, charges or other encumbrances of any
         nature whatsoever (collectively "LIENS").

              (d) Except as set forth in Schedule 2.3, there are no outstanding
         bonds, debentures, notes or other indebtedness or other securities of
         the Company having the right to vote (or convertible into, or
         exchangeable for, securities having the right to vote) on any matters
         on which stockholders of the Company may vote.

              (e) Except for the Transaction Documents (as hereinafter defined)
         or as set forth in Schedule 2.3, the Company is not a party to any
         agreement or arrangement restricting the voting or transfer of any
         outstanding shares of the Common Stock or Preferred Stock of the
         Company. (a)

              (f) Except as set forth in Schedule 2.3 or in the Transaction
         Documents and as provided by statutes of general application, there are
         no legal, contractual or other restrictions on the payment of dividends
         or other distributions or amounts on or in respect of any of the Common
         Stock or Preferred Stock of the Company.

              (g) Except as set forth in Schedule 2.3 or in the Transaction
         Documents, there are no agreements or arrangements to which the Company
         or any of its subsidiaries is a

<PAGE>
                                                                 Page 149 of 229

         party pursuant to which the Company is or could be required to register
         shares of Common Stock or other securities under the Securities Act.

              (h) All outstanding shares of Common Stock and Preferred Stock of
         the Company were issued in compliance with the registration provisions
         of or were exempt from registration under applicable federal and state
         securities laws.

         Section 2.4 AUTHORITY RELATIVE TO THIS AGREEMENT AND DGCL SECTION 203.

              (a) The Company has all necessary corporate power and authority to
         execute and deliver this Agreement, the Notes, the Registration Rights
         Agreement in the form of Exhibit F hereto among the Company and the
         Purchasers (the "REGISTRATION RIGHTS AGREEMENT"), the Standstill
         Agreement dated as of the date hereof among the Company and the
         Purchasers (the "STANDSTILL AGREEMENT"), and the Warrants (as defined
         in Section 6.3) (collectively, the "TRANSACTION DOCUMENTS"), and to
         perform its obligations under the Transaction Documents and to
         consummate the transactions contemplated thereby. The execution and
         delivery of the Transaction Documents by the Company and the
         consummation by the Company of the transactions contemplated thereby
         have been duly and validly authorized by all necessary corporate
         action, and no other corporate proceedings on the part of the Company
         are necessary to authorize or to consummate the transactions so
         contemplated (other than the adoption and filing of the Certificate of
         Designation and the approval of the Stock Purchase by the stockholders
         as contemplated herein). The Board has determined that it is advisable
         and in the best interest of the Company's stockholders for the Company
         to consummate the Stock Purchase upon the terms and subject to the
         conditions of this Agreement, and, except for Messrs. Fillat and
         Murray, who abstained, has unanimously recommended that the Company's
         stockholders approve and adopt this Agreement. Each of the Transaction
         Documents has been duly and validly executed and delivered by the
         Company and, assuming the due authorization, execution and delivery by
         the Purchasers, constitutes a legal, valid and binding obligation of
         the Company enforceable against the Company in accordance with its
         terms, except that (i) such enforcement may be subject to bankruptcy,
         insolvency, reorganization, moratorium or other similar laws now or
         hereafter in effect relating to creditors' rights, (ii) the remedy of
         specific performance and injunctive and other forms of equitable relief
         may be subject to equitable defenses and to the discretion of the court
         before which any proceeding therefor may be brought, and (iii) the
         enforcement of the indemnification provisions contained in the
         Registration Rights Agreement are subject to applicable securities laws
         and principles of public policy.

              (b) The Board has taken all actions so that the restrictions
         contained in Section 203 of the Delaware General Corporation Law, as
         from time to time in effect, applicable to a "business combination" (as
         defined in Section 203) will not apply to the execution, delivery or
         performance of this Agreement by the interested stockholders (as
         defined in Section 203) or their consummation of the transactions
         contemplated hereby.
<PAGE>
                                                                 Page 150 of 229

         Section 2.5       NO CONFLICT; REQUIRED FILINGS AND CONSENTS.

              (a) The Company has made available to the Purchasers copies of (i)
         all loan agreements, indentures, mortgages, pledges, conditional sale
         or title retention agreements, security agreements, equipment
         obligations, guaranties, standby letters of credit, equipment leases or
         lease purchase agreements to which the Company or any of its
         subsidiaries is a party or by which any of them is bound, each in a
         principal outstanding amount equal to or exceeding $2,000,000, but
         excluding any such agreement between the Company and its wholly-owned
         subsidiaries or between two or more wholly-owned subsidiaries of the
         Company; (ii) all contracts, agreements, commitments or other
         understandings or arrangements to which the Company or any of its
         subsidiaries is a party or by which any of them or any of their
         respective properties or assets are bound or affected, but excluding
         contracts, agreements, commitments or other understandings or
         arrangements entered into in the ordinary course of business and
         involving, in each case, aggregate payments or receipts by the Company
         or any of its subsidiaries of less than $2,000,000 in any single
         instance; and (iii) all agreements which, as of the date hereof, are
         required to be filed by the Company as "material contracts" with the
         Securities Exchange Commission ("SEC") pursuant to the requirements of
         the Securities Exchange Act of 1934, as amended, and the SEC's rules
         and regulations thereunder (the "EXCHANGE ACT") (collectively, the
         "MATERIAL CONTRACTS"). Schedule 2.5 sets forth a correct and complete
         list of the Material Contracts.

              (b) Except as set forth in Schedule 2.5, (i) neither the Company
         nor any of its subsidiaries has breached, is in default under, or has
         received written notice of any breach of or default under, any Material
         Contract, (ii) to the knowledge of the Company, no other party to any
         of the Material Contracts has breached or is in default of any of its
         obligations thereunder, and (iii) each of the Material Contracts is in
         full force and effect and constitutes a legal, valid and binding
         obligation of the parties thereto enforceable against such parties in
         accordance with its terms, except in any such case for breaches,
         defaults or failures to be in full force and effect that do not
         constitute a Material Adverse Effect. Except as set forth in Schedule
         4.7, the execution and delivery of this Agreement by the Company does
         not, and the performance of this Agreement by the Company will not,
         constitute a breach of or default under any Material Contract, or
         require any consent pursuant to any Material Contract, except where the
         failure to obtain such consent does not constitute a Material Adverse
         Effect or materially adversely affect the Purchasers with respect to
         their rights under the Transaction Documents.

              (c) The execution and delivery of this Agreement by the Company
         does not, and the performance of this Agreement by the Company and the
         consummation of the transactions contemplated hereby will not, (i)
         conflict with or violate the Certificate of Incorporation or By-Laws of
         the Company, (ii) conflict with or violate any federal, foreign, state
         or provincial law, rule, regulation, order, judgment or decree
         (collectively, "LAWS") applicable to the Company or any of

<PAGE>
                                                                 Page 151 of 229

         its subsidiaries or by which its or any of their respective properties
         are bound or affected, or (iii) except as set forth on Schedule 4.7,
         result in any breach of or constitute a default (or an event that with
         notice or lapse of time or both would become a default under), or
         impair the Company's or any of its subsidiaries' rights or alter the
         rights or obligations of any third party under, or give to others any
         rights of termination, amendment, acceleration or cancellation of, or
         result in the creation of a Lien on any of the properties or assets of
         the Company or any of its subsidiaries pursuant to any Material
         Contract, except in any such case for any such conflicts, violations,
         breaches, defaults or other occurrences that do not constitute a
         Material Adverse Effect.

              (d) Except as set forth on Schedule 2.5, the execution and
         delivery of this Agreement by the Company does not, and the performance
         of this Agreement by the Company will not, require any consent,
         approval, authorization or permit of, or filing with or notification
         to, any federal, foreign, state or provincial governmental or
         regulatory authority except (i) for applicable requirements, if any, of
         the Securities Act, the Exchange Act, state securities laws ("BLUE SKY
         LAWS") and the pre-merger notification requirements of the
         Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended (the
         "HSR Act"), (ii) applicable requirements of the Communications Act (as
         hereinafter defined) and the FCC (as hereinafter defined), (iii) filing
         of the Certificate of Designation, and (iv) where the failure to obtain
         such consents, approvals, authorizations or permits, or to make such
         filings or notifications, would not prevent or delay consummation of
         the Closing, or otherwise prevent or delay the Company from performing
         its obligations under this Agreement, or would not otherwise have a
         Material Adverse Effect.

         Section 2.6       COMPLIANCE.

              (a) Neither the Company nor any of its subsidiaries is in conflict
         with, or in default or violation of, (i) any Law applicable to the
         Company or any of its subsidiaries or by which its or any of their
         respective properties are bound or affected or (ii) any Material
         Contract, except for any such conflicts, defaults or violations which
         do not constitute a Material Adverse Effect.

              (b) Each of the Company and its subsidiaries has filed or caused
         to be filed with each applicable Governmental Body all reports,
         applications, documents, instruments and information required to be
         filed by it pursuant to all applicable laws, rules, regulations,
         ordinances, judgment, decrees, rulings, orders, awards, injunctions,
         recommendations or other official actions of any Governmental Body,
         other than those as to which the failure to file do not constitute a
         Material Adverse Effect.

         Section 2.7       SEC FILINGS; FINANCIAL STATEMENTS.

              (a) The Company has filed with the Securities and Exchange
         Commission all reports, schedules, forms, statements and other
         documents required by the Securities Act

<PAGE>
                                                                 Page 152 of 229

         or the Exchange Act to be filed by the Company since January 1, 1998 as
         filed on or before the date of this Agreement (collectively, and in
         each case including all exhibits and schedules thereto and documents
         incorporated by reference therein the "COMPANY SEC REPORTS"). Schedule
         2.7 sets forth a list of all Company SEC Reports. As of their
         respective dates (except if revised or superseded by a subsequent
         filing on or before the date of this Agreement, as of such date), the
         Company SEC Reports (including the financial statements included
         therein) (i) complied as to form in all material respects with the
         requirements of the Securities Act or the Exchange Act, as the case may
         be, and the rules and regulations thereunder, and (ii) did not contain
         any untrue statement of a material fact or omit to state a material
         fact required to be stated therein or necessary in order to make the
         statements therein, in light of the circumstances under which they were
         made, not misleading. The Company has filed with the Securities and
         Exchange Commission as exhibits to the Company SEC Reports all
         agreements, contracts and other documents or instruments required to be
         so filed, and such exhibits are in all material respects true and
         complete copies of such agreements, contracts and other documents or
         instruments, as the case may be (subject to any confidential treatment
         requests allowing excision of confidential information from the
         publicly filed document). None of the subsidiaries of the Company is
         required to file any reports, schedules, statements or other documents
         with the Securities and Exchange Commission.

              (b) The consolidated balance sheets of the Company and its
         consolidated subsidiaries as of each of December 31, 1998 and March 31,
         1999 and the related consolidated statements of income (loss) and
         stockholders' equity and cash flows for the 12 month period and three
         month period then ended, true and complete copies of which have been
         delivered to the Purchasers, fairly present the consolidated financial
         position of the Company and its consolidated subsidiaries as of their
         respective dates and their consolidated results of operations and cash
         flows for the respective periods then ended, in accordance with U.S.
         generally accepted accounting principles applied on a consistent basis
         except as described in the footnotes to the financial statements or as
         disclosed in Schedule 2.7.

              (c) The Company has made available to the Purchasers copies of
         each management letter delivered to any of the Company and its
         subsidiaries by PricewaterhouseCoopers LLP in connection with the
         financial statements referred to in this Section 2.7 or relating to any
         review by them of the internal controls of the Company and its
         subsidiaries during the twelve months ended December 31, 1998 or
         thereafter, and has made available for inspection for the twelve month
         period ended December 31, 1998 and, subject to the approval of
         PricewaterhouseCoopers LLP, after the date of this Agreement will make
         available for inspection all reports and working papers produced or
         developed by them or management in connection with their examination of
         those financial statements and the other financial statements for the
         three years then ended, as well as all such reports and working papers
         for prior periods for which any liability of any of the Company and its
         subsidiaries for Taxes (as hereinafter defined) has not been finally
         determined or barred by applicable statutes of limitation.

<PAGE>

<PAGE>
                                                                 Page 154 of 229

              (d) Since January 1, 1998, to the knowledge of the Company, there
         has been no material disagreement (within the meaning of Item
         304(a)(1)(iv) of Regulation S-K under the Securities Act) between the
         Company and its independent accountants with respect matters of
         accounting principles or practices, financial statement disclosure or
         auditing scope or procedures which if not resolved to the satisfaction
         of such accountant would cause it to make a reference to the subject
         matter of the disagreements in connection with its report.

         Section 2.8 ABSENCE OF CERTAIN CHANGES OR EVENTS. Except as set forth
in Schedule 2.8 or in the Company SEC Reports or as contemplated by this
Agreement, since December 31, 1998, the Company has conducted its business in
the ordinary course and there has not occurred: (a) any Material Adverse Effect;
(b) any amendments or changes in the Certificate of Incorporation or By-Laws of
the Company; (c) any damage to, destruction or loss of any asset of the Company
(whether or not covered by insurance) that could reasonably be expected to have
a Material Adverse Effect; (d) any material change by the Company in its
accounting methods, principles or practices; (e) any material revaluation by the
Company of any of its assets, including, without limitation, writing down the
value of inventory or writing off notes or accounts receivable other than in the
ordinary course of business; or (f) any sale of a material amount of property of
the Company or any of its subsidiaries, except in the ordinary course of
business.

         Section 2.9 NO UNDISCLOSED LIABILITIES. Except as set forth in the
Company SEC Reports or on Schedule 2.9, neither the Company nor any of its
subsidiaries has any liabilities (absolute, accrued, contingent or otherwise),
except liabilities (a) in the aggregate adequately provided for in the Company's
audited balance sheet (including any related notes thereto) for the fiscal year
ended December 31, 1998 included in the Company SEC Reports (the "1998 COMPANY
BALANCE SHEET"), (b) incurred in the ordinary course of business and not
required under U.S. generally accepted accounting principles to be reflected on
the 1998 Company Balance Sheet, (c) incurred since December 31, 1998 in the
ordinary course of business consistent with past practice, (d) incurred in
connection with this Agreement, or (e) which do not constitute a Material
Adverse Effect.

         Section 2.10 ABSENCE OF LITIGATION. There are no claims, actions,
suits, proceedings or investigations pending or, to the knowledge of the
Company, threatened against the Company or any of its subsidiaries, or any
properties or rights of the Company or any of its subsidiaries, before any
federal, foreign, state or provincial court, arbitrator or administrative,
governmental or regulatory authority or body that could reasonably be expected
to have a Material Adverse Effect.

         Section 2.11 EMPLOYEE BENEFIT PLANS. Except as set forth in Schedule
2.11 and in the Company SEC Reports:
<PAGE>
                                                                 Page 155 of 229

              (a) The Company and its subsidiaries are not and have not been
         required to contribute to any employee benefit plan or any other profit
         sharing, stock option, stock purchase, stock appreciation, deferred
         compensation, severance, or other material plan or arrangement for the
         benefit of the Company, its subsidiaries and current or former
         directors, officers, or employees (collectively "EMPLOYEE PLANS").

              (b) None of the Company and its subsidiaries has incurred, or has
         any reason to expect that it will incur, any liability to the Pension
         Benefit Guaranty Corporation (other than premium payments) or otherwise
         under Title IV of the Employee Retirement Income Security Act of 1974,
         as amended ("ERISA") (including any withdrawal liability) or under the
         Internal Revenue Code of 1986, as amended (the "CODE") with respect to
         any such employee benefit plan which is an employee pension benefit
         plan.

              (c) Each Employee Plan maintained by the Company is, and has been
         at all times, maintained and operated in compliance with all statutes,
         orders or governmental rules or regulations, including but not limited
         to ERISA, the Code and applicable federal or state securities laws, and
         any and all collective bargaining agreements and other contracts
         applicable thereto and there have been no acts or omissions by the
         Company, its subsidiaries or its officers which have given rise to or
         could reasonably be expected to give rise to fines, penalties, taxes or
         related charges or liability under ERISA or the Code, except where such
         charges and liabilities do not constitute a Material Adverse Effect.

              (d) All plans and related trusts that are intended to qualify
         under Sections 401(a) and 501(a) of the Code, have been determined by
         the Internal Revenue Service to be so qualified, and copies of such
         determination letters have been made available to the Purchasers.

         Section 2.12 PROXY STATEMENT. The information supplied by the Company
for inclusion in the proxy statement to be sent to the stockholders of the
Company in connection with the meeting of the stockholders of the Company to
consider the sale of the Shares (the "STOCKHOLDERS MEETING") (such proxy
statement as amended or supplemented is referred to herein as the "PROXY
STATEMENT"), will not, on the date the Proxy Statement (or any amendment thereof
or supplement thereto) is first mailed to stockholders or at the time of the
Stockholders Meeting, contain any untrue statement of a material fact, or shall
omit to state any material fact necessary in order to make the statements made
therein not false or misleading, or omit to state any material fact necessary to
correct any statement in any earlier communication with respect to the
solicitation of proxies for the Stockholders Meeting which has become false or
misleading. If at any time prior to the Closing Date any event relating to the
Company or any of its affiliates, officers or directors should be discovered by
the Company which is required to be set forth in a supplement to the Proxy
Statement, the Company shall promptly inform the Purchasers and shall amend such
Proxy Statement to correct such omission. Notwithstanding the foregoing, the
Company makes no representation or warranty with respect to any statement or
omission based on information supplied by the Purchasers which is contained in
any of the foregoing documents.

<PAGE>
                                                                 Page 156 of 229

         Section 2.13      TITLE TO PROPERTY.

              (a) Except as set forth in Schedule 2.13 or in the Company SEC
         Reports, the Company and each of its subsidiaries have good and
         marketable title to all of their properties and assets, free and clear
         of all liens, charges and encumbrances, except liens for taxes not yet
         due and payable and such liens or other imperfections of title which do
         not constitute a Material Adverse Effect; and, to the knowledge of the
         Company, all leases pursuant to which the Company or any of its
         subsidiaries lease from others material amounts of real or personal
         property, are in good standing, valid and effective in accordance with
         their respective terms, and there is not, to the knowledge of the
         Company, under any of such leases, any existing default or event of
         default (or event which with notice or lapse of time, or both, would
         constitute a default), except where such default or event of default
         does not constitute a Material Adverse Effect.

              (b) All tangible Company properties are in such condition and
         repair, and are suitable, sufficient in amount, size and type and so
         situated, as is appropriate and adequate for the uses for which they
         are used and intended and to carry on the business of the Company or
         such subsidiary, as the case may be, as now conducted.

         Section 2.14 RESTRICTIONS ON BUSINESS ACTIVITIES. Except as set forth
in the Company SEC Reports or on Schedule 2.14, to the Company's knowledge,
there is no agreement, judgment, injunction, order or decree binding upon the
Company or any of its subsidiaries which has or could reasonably be expected to
have the effect of prohibiting or impairing any business practice of the Company
or any of its subsidiaries, acquisition of property by the Company or any of its
subsidiaries or the conduct of business by the Company or any of its
subsidiaries as currently conducted or as proposed to be conducted by the
Company, except for any prohibition or impairment as does not constitute a
Material Adverse Effect.

         Section 2.15      TAXES.

              (a) For purposes of this Agreement, "TAX" or "TAXES" shall mean
         taxes, fees, levies, duties, tariffs, imposts, and governmental
         impositions or charges of any kind in the nature of (or similar to)
         taxes, payable to any federal, state, local or foreign taxing
         authority, including (without limitation) (i) income, franchise,
         profits, gross receipts, AD VALOREM, net worth, value added, sales,
         use, service, real or personal property, special assessments, capital
         stock, license, payroll, withholding, employment, social security,
         workers' compensation, unemployment compensation, utility, severance,
         production, excise, stamp, occupation, premiums, windfall profits,
         transfer and gains taxes, and (ii) interest, penalties, additional
         taxes and additions to tax imposed with respect thereto; and "TAX
         RETURNS" shall mean returns, reports, and information statements with
         respect to Taxes required to be filed with the Internal Revenue Service
         or any other federal, foreign, state or provincial taxing authority,
         domestic or foreign, including, without limitation, consolidated,
         combined and unitary tax returns.
<PAGE>
                                                                 Page 157 of 229

              (b) Except as set forth in the Company SEC Reports: (i) The
         Company and its subsidiaries have filed all Tax Returns required to be
         filed by them, except where the failure to file a Tax Return does not
         constitute a Material Adverse Effect and (ii) the Company and its
         subsidiaries have paid all Taxes covered by such Tax Returns and have
         paid all other Taxes as are due, except those with respect to which the
         Company is maintaining adequate reserves, unless the failure to do so
         does not constitute a Material Adverse Effect. Except as set forth in
         the Company SEC Reports or except as does not involve or would not
         result in liability to the Company or any of its subsidiaries that
         could reasonably be expected to have a Material Adverse Effect: (i)
         there are no tax liens on any assets of the Company or any subsidiary
         thereof; and (ii) neither the Company nor any of its subsidiaries has
         granted any waiver of any statute of limitations with respect to, or
         any extension of a period for the assessment of, any Tax. The accruals
         and reserves for Taxes (including deferred taxes) reflected in the 1998
         Company Balance Sheet are in all material respects adequate to cover
         all Taxes required to be accrued through the date thereof (including
         interest and penalties, if any, thereon and Taxes being contested) in
         accordance with U.S. generally accepted accounting principles.

         Section 2.16 ENVIRONMENTAL MATTERS. Except in all cases as, in the
aggregate, do not constitute a Material Adverse Effect, and except for any
matters as to which remediation efforts have been completed, the Company and
each of its subsidiaries to the Company's knowledge: (i) have obtained all
franchises, grants, authorizations, licenses, permits, consents, approvals and
orders ("APPROVALS") which are required to be obtained under all applicable
federal, state, foreign or local laws or any regulation, code, plan, order,
decree, judgment, notice or demand letter issued, entered, promulgated or
approved thereunder relating to pollution or protection of the environment,
including laws relating to emissions, discharges, releases or threatened
releases of pollutants, contaminants, or hazardous or toxic materials or wastes
into ambient air, surface water, ground water, or land or otherwise relating to
the manufacture, processing, distribution, use, treatment, storage, disposal,
transport, or handling of pollutants, contaminants or hazardous or toxic
materials or wastes by the Company or its subsidiaries or their respective
agents ("ENVIRONMENTAL LAWS"); (ii) each of such Approvals is in full force and
effect and each of the Company and each of its subsidiaries in compliance with
all terms and conditions of such required Approvals and also is in compliance
with all other limitations, restrictions, conditions, standards, prohibitions,
requirements, obligations, schedules and timetables contained in applicable
Environmental Laws; (iii) as of the date hereof, are not aware of nor have
received notice of any past or present violations of Environmental Laws or any
event, condition, circumstance, activity, practice, incident, action or plan
which is reasonably likely to interfere with or prevent continued compliance
with or which would give rise to any common law or statutory liability, or
otherwise form the basis of any claim, action, suit or proceeding, against the
Company or any of its subsidiaries based on or resulting from the manufacture,
processing, distribution, use, treatment, storage, disposal, transport or
handling, or the emission, discharge or release into the environment, of any
pollutant, contaminant or hazardous or toxic material or waste; and (iv) have
taken all actions necessary under applicable Environmental Laws to register

<PAGE>
                                                                 Page 158 of 229

any products or materials required to be registered by the Company or its
subsidiaries (or any of their respective agents) thereunder.

         Section 2.17      INTELLECTUAL PROPERTY.

              (a) To its knowledge, the Company, directly or indirectly, owns,
         or is licensed or otherwise possesses (or has applied for), legally
         enforceable rights to use, all copyrights, uncopyrighted works,
         trademarks, trademark rights, service marks, trade names, trade name
         rights, patents, patent rights, unpatented inventions, licenses,
         permits, trade secrets, know-how, inventions, computer software,
         seismic data and intellectual property rights and other proprietary
         rights together with applications and licenses for any of the foregoing
         (the "COMPANY INTELLECTUAL PROPERTY RIGHTS"), except where the failure
         to so own, be licensed or otherwise possess legally enforceable rights
         to use does not constitute a Material Adverse Effect.

              (b) No claims with respect to the Company Intellectual Property
         Rights have been asserted or, to the knowledge of the Company, are
         threatened by any person, that reasonably would be expected to have a
         Material Adverse Effect on the Company or any of its subsidiaries, (i)
         to the effect that the manufacture, sale, licensing or use of any of
         the products of the Company or any of its subsidiaries as now
         manufactured, sold or licensed or used or currently proposed for
         manufacture, use, sale or licensing by the Company or any of its
         subsidiaries infringes on any copyright, patent, trademark, service
         mark or trade secret, (ii) against the use by the Company or any of its
         subsidiaries of any material trademarks, service marks, trade names,
         trade secrets, copyrights, patents, technology, know-how or computer
         software programs and applications used in the business of the Company
         and its subsidiaries as currently conducted, or (iii) challenging the
         ownership, validity or effectiveness of any of the Company Intellectual
         Property Rights. All registered trademarks, service marks and
         copyrights held by the Company are valid and subsisting. To the
         knowledge of the Company, there is no unauthorized use, infringement or
         misappropriation of any of the Company Intellectual Property Rights by
         any third party, including any employee or former employee of the
         Company or any of its subsidiaries, which could reasonably be expected
         to have a Material Adverse Effect. No Company Intellectual Property
         Right or product of the Company or any of its subsidiaries is subject
         to any outstanding decree, order, judgment, or stipulation restricting
         in any manner the licensing thereof by the Company or any of its
         subsidiaries.

              (c) To the best of the Company's knowledge, none of the hardware
         or software currently owned, leased or licensed by the Company and used
         or proposed to be used in the business and operations of any of the
         Company and its subsidiaries contains imbedded logic or code that will
         fail to recognize the year 2000 as such, or that might fail or cause
         other hardware or software to cease to perform according to
         specifications or to the needs of the business of the Company or the
         subsidiary, as the case might be, by reason of the date change after
         December 31, 1999, except where such condition does not constitute a
         Material Adverse Effect.

<PAGE>
                                                                 Page 159 of 229

         Section 2.18 CERTAIN AGREEMENTS OF OFFICERS AND EMPLOYEES. To the
Company's knowledge, no employee of the Company is, or is now expected to be, in
violation of any term of any employment contract, patent disclosure agreement,
non-competition agreement, or any other contract or agreement or any restrictive
covenant relating to the right of any such officer or employee to be employed by
the Company because of the nature of the business conducted or to be conducted
by the Company or relating to the use of trade secrets or proprietary
information of others.

         Section 2.19 REGULATORY MATTERS Except to the extent as would not have
a Material Adverse Effect and except as set forth in Schedule 2.19:

              (a) The Company and its subsidiaries are in compliance with the
         Communications Act of 1934, as amended by the Telecommunications Act of
         1996 (the "COMMUNICATIONS ACT") and with all applicable rules,
         regulations and policies of the Federal Communications Commission (the
         "FCC").

              (b) Schedule 2.19 sets forth a complete and accurate list of all
         licenses (the "FCC LICENSES") granted to the Company and its
         subsidiaries by the FCC. All the FCC Licenses are currently valid and
         in full force and effect and the Company and its subsidiaries have met
         material applicable construction or build-out regulations required to
         be met as of this date for each of the FCC Licenses. Neither the
         Company nor any of its subsidiaries has received any notification of an
         investigation, violation or forfeiture, any notice of apparent
         liability, or any other order or complaint issued by or before any
         court or governmental body, including the FCC that could in any manner
         threaten or adversely affect the validity, continued effectiveness,
         material terms, or likelihood of renewal of any of the FCC Licenses,
         nor to the knowledge of the Company is any such action threatened.
         Neither the Company nor any of its subsidiaries has knowledge of any
         other proceedings (other than proceedings relating to the wireless
         communications or 38 GHz industries generally) that could in any manner
         threaten or adversely affect the validity, continued effectiveness,
         material terms, or likelihood of renewal of any of the FCC Licenses.

              (c) No event has occurred or failed to occur which (i) results in,
         or after notice or lapse of time or both would result in, revocation,
         suspension, adverse modification, non-renewal, impairment, restriction
         or termination of, or order of forfeiture with respect to, any FCC
         License or (ii) adversely affects or could reasonably be expected in
         the future to adversely affect any of the rights of the Company or any
         of its subsidiaries thereunder except for legislation or rule making of
         general applicability.

              (d) The Company and its subsidiaries have duly filed in a timely
         manner all filings, reports, applications, documents, instruments and
         information required to be filed by them under the Communications Act
         or the applicable rules, regulations and policies of the FCC, and all
         such filings are true, correct and complete in all material respects.
<PAGE>
                                                                 Page 160 of 229

              (e) Neither the Company nor any of its subsidiaries has any reason
         to believe that any of the FCC Licenses will not be renewed in the
         ordinary course.

         Section 2.20 RANK OF NOTES. The Notes rank and will rank on a parity in
right of payment with all senior indebtedness of the Company outstanding on the
date hereof or that may be incurred hereafter.

         Section 2.21 INTERESTED PARTY TRANSACTIONS. Except as contemplated by
this Agreement or as set forth on Schedule 2.21, since December 31, 1998, no
event has occurred that would be required to be reported as a Certain
Relationship or Related Transaction pursuant to Item 404 of Regulation S-K
promulgated by the SEC.

         Section 2.22 INSURANCE. The Company and its subsidiaries maintain in
full force and effect insurance policies with reputable insurance carriers. Such
policies provide adequate coverage for all normal risks incident to the business
of the Company and its subsidiaries and their respective properties and assets
and are in character and amount similar to that carried by entities engaged in
similar businesses and subject to the same or similar perils or hazards, except
as do not constitute a Material Adverse Effect.

         Section 2.23 BROKERS. No broker, finder or investment banker (other
than Morgan Stanley & Co. Incorporated ("MORGAN STANLEY"), the fees and expenses
of which will be paid by the Company) is entitled to any brokerage, finder's or
other fee or commission in connection with the transactions contemplated by this
Agreement based upon arrangements made by or on behalf of the Company or its
subsidiaries or affiliates. The Company has heretofore made available to the
Purchasers a complete and correct copy of all agreements between the Company and
Morgan Stanley pursuant to which such firm would be entitled to any payment
relating to the transactions contemplated hereunder.

         Section 2.24 DISCLOSURE. This agreement including the schedules and
exhibits hereto and the certificates delivered hereunder does not, and at
Closing will not, contain any untrue statement of a material fact, or omit to
state a material fact necessary to make the statements herein, in light of the
circumstances under which they were made, not misleading. With respect to
projections contained in the Business Strategy Plan (as hereinafter defined),
the Company notes that actual results may vary materially from the projections
and represents only that such projections were prepared in good faith and are
based on a set of assumptions believed by the Company to be reasonable as of the
date hereof.

         Section 2.25 SECURITIES LAWS. Assuming that each of the Purchaser's
representations and warranties contained in Article III hereof are, and continue
to be at the Closing Date and at the date of exercise of the Warrants, true and
correct, the issuance and sale of the Notes and the Warrants are as of the date
hereof, and the issuance and sale of the Shares on the Closing Date will be, and
the issuance of the shares of Common Stock upon conversion of the Preferred
Stock

<PAGE>
                                                                 Page 161 of 229

will be, exempt from the registration and prospectus delivery requirements of
the Securities Act and from registration and qualification under applicable Blue
Sky Laws.

         Section 2.26 ACQUIRING PERSON. Assuming that each of the Purchaser's
representations and warranties contained in Article III hereof are at the
Closing Date true and correct, at the Closing Date no Purchaser will constitute
an Acquiring Person as defined in the Rights Agreement dated as of June 20, 1997
between the Company and BankBoston, NA as Rights Agent.

         Section 2.27 ACCELERATION. Except as set forth on Schedule 2.27, the
execution and performance of this Agreement will not in and of itself result in
the acceleration of the vesting of any options issued by the Company or the
payments by the Company to any employee, officer or director.

         Section 2.28 BOARD OF DIRECTORS. Schedule 2.28 sets forth the Company's
directors as of the date hereof, and the nominating class of each such director.


                                  ARTICLE III.

                REPRESENTATIONS AND WARRANTIES OF THE PURCHASERS

         Subject to Section 7.1 hereof, each of the Purchasers severally
represents and warrants to the Company that:

         Section 3.1 ORGANIZATION. Such Purchaser is duly organized, validly
existing and in good standing under the laws of the jurisdiction of its
organization, with all requisite power and authority to own, lease and operate
its properties and to conduct its business as now being conducted.

         Section 3.2 DUE AUTHORIZATION. Such Purchaser has all right, power and
authority to enter into this Agreement, the Registration Rights Agreement and
the Standstill Agreement and to consummate the transactions contemplated hereby
and thereby. The execution and delivery of this Agreement, the Registration
Rights Agreement and the Standstill Agreement by such Purchaser and the
consummation by such Purchaser of the transactions contemplated hereby and
thereby have been duly authorized by all necessary action on behalf of such
Purchaser. Each of this Agreement, the Registration Rights Agreement and the
Standstill Agreement has been duly executed and delivered by such Purchaser and
constitutes the valid and binding agreement of such Purchaser enforceable in
accordance with its terms, except that (i) such enforcement may be subject to
bankruptcy, insolvency, reorganization, moratorium or other similar laws now or
hereafter in effect relating to creditors' rights, (ii) the remedy of specific
performance and injunctive and other form of equitable relief may be subject to
equitable defenses and to the discretion of the court before which any
proceeding therefor may be brought, and (iii) the

<PAGE>
                                                                 Page 162 of 229

enforcement of the indemnification provisions contained in the Registration
Rights Agreement are subject to applicable securities laws and principles of
public policy.

         Section 3.3 ACQUISITION FOR INVESTMENT. Such Purchaser is acquiring the
Shares being purchased by it for its own account for the purpose of investment
and not with a view to or for sale in connection with any distribution thereof,
and such Purchaser has no present intention or plan to effect any distribution
of Shares other than pursuant to Rule 144A under the Securities Act or in an
offering registered under the Securities Act. Such Purchaser does not have any
contract, undertaking, agreement or arrangement with any person to sell,
transfer, or grant participations to such person or to any third person, with
respect to any of the Shares.

         Section 3.4 BROKERS OR FINDERS. No agent, broker, investment banker or
other firm or Person acting on behalf of such Purchaser, including any of the
foregoing that is an affiliate of such Purchaser, is or will be entitled to any
broker's or finder's fee or any other commission or similar fee in connection
with any of the transactions contemplated by this Agreement.

         Section 3.5 ACCREDITED INVESTOR. Such Purchaser is an "accredited
investor" within the meaning of Regulation D under the Securities Act.

         Section 3.6 FINANCIAL CONDITION. Such Purchaser's financial condition
is such that it is able to bear the risk of holding the Shares for an indefinite
period of time and can bear the loss of its entire investment in the Shares.

         Section 3.7 EXPERIENCE. Such Purchaser has such knowledge and
experience in financial and business matters and in making high risk investments
of this type that it is capable of evaluating the merits and risks of the
purchase of Shares.

         Section 3.8 NON-U.S. OWNERSHIP. To the knowledge of such Purchaser,
except as set forth on Schedule 3.8, the percentage of the capital stock or
ownership or voting interests of such Purchaser that, for purposes of Section
3.10(b) of the Communications Act is owned or voted, directly or indirectly,
beneficially or otherwise, by foreign entities or persons, does not exceed 25%.

         Section 3.9 BENEFICIAL OWNERSHIP. Each Purchaser that is a party to the
Standstill Agreement represents that as of the date hereof it has not entered
into any agreement, other than the "Stockholders Agreement" (as defined in the
Standstill Agreement) and the Transaction Documents, with respect to the
acquisition, voting or disposition of the Shares with any party.

         Section 3.10 AFFILIATES. Except for securities such Purchaser has
agreed to purchase hereunder or as set forth on Schedule III, such Purchaser
does not beneficially own, directly or indirectly, beneficially, any of the
Company's capital stock.

         Section 3.11 PROXY STATEMENT. The information supplied by such
Purchaser in writing specifically for inclusion in the Proxy Statement will not,
on the date the Proxy Statement (or
<PAGE>
                                                                 Page 163 of 229

any amendment thereof or supplement thereto) is first mailed to stockholders or
at the time of the Stockholders Meeting, contain any untrue statement of a
material fact, or shall omit to state any material fact necessary in order to
make such information not false or misleading. If at any time prior to the
Closing Date any event relating to such Purchaser or any of its affiliates,
officers or directors should be discovered by such Purchaser which is required
to be set forth in a supplement to the Proxy Statement, such Purchaser shall
promptly inform the Company.


                                  ARTICLE IV.

                              ADDITIONAL AGREEMENTS

         The Company and each of the Purchasers severally agree that:

         Section 4.1 HSR ACT. As promptly as practicable after the date of the
execution of this Agreement, the Company, those Purchasers required by law to
file and all other necessary parties shall file notifications under and in
accordance with the HSR Act in connection with the Stock Purchase and the
transactions contemplated hereby and shall respond as promptly as practicable to
any inquiries and requests received (i) from the Federal Trade Commission (the
"FTC") and the Antitrust Division of the Department of Justice (the "ANTITRUST
DIVISION") for additional information or documentation or (ii) from any State
Attorney General or other governmental authority in connection with antitrust
matters.

         Section 4.2 PROXY STATEMENT. Unless the Closing is to occur without a
vote of the Company's stockholders, the Company shall use its best efforts, to
prepare and file with the SEC as promptly as possible preliminary proxy
materials seeking stockholder approval of the Stock Purchase (the "PROXY
STATEMENT"). The Purchasers shall use their best efforts to furnish the Company
such information about the Purchasers and the directors proposed by the
Purchasers as may be necessary to prepare and file the definitive Proxy
Statement on such schedule. As promptly as practicable after comments are
received from the SEC thereon and after the furnishing by the Company and the
Purchasers of all information required to be contained therein, the Company
shall use its reasonable best efforts to mail the Proxy Statement to its
stockholders, as soon thereafter as practicable. The Proxy Statement shall
include the recommendation of the Board in favor of the Stock Purchase, subject
to Section 4.4.

         Section 4.3 STOCKHOLDERS MEETING. Unless the Closing is to occur
without a vote of the Company's stockholders, the Company shall call and hold
its Stockholders Meeting as promptly as practicable and in accordance with
applicable laws for the purpose of voting upon the approval of the Stock
Purchase. Except as contemplated by Section 4.4, the Company shall use all
reasonable efforts to solicit from its stockholders proxies in favor of adoption
of this Agreement and approval of the transactions contemplated hereby and shall
take all other action necessary or advisable to secure the vote or consent of
stockholders to obtain such approvals.
<PAGE>
                                                                 Page 164 of 229

         Section 4.4 ALTERNATIVE TRANSACTIONS. The Company shall not, or permit
any of its officers, directors, employees, financial advisors and other
representatives on behalf of the Company to:

                           (1) enter into any agreement or other arrangement
         with respect to, or take any other action to effect, any Alternative
         Transaction (as hereinafter defined);

                           (2) solicit, initiate or encourage (including,
         without limitation, by way of furnishing information), or take any
         other action to facilitate, any inquiry or the making of any proposal
         to any of the Company, its subsidiaries and its stockholders from any
         person which constitutes, or may reasonably be expected to lead to, a
         proposal with respect to an Alternative Transaction with respect to any
         of the Company and its subsidiaries, or endorse any Alternative
         Transaction; or

                           (3) continue, enter into or participate in any
         activities, discussions or negotiations regarding any of the foregoing,
         or furnish to any other person any information with respect to the
         business, properties, operations, prospects or condition (financial or
         otherwise) of any of the Company and its subsidiaries or any of the
         foregoing, or otherwise cooperate in any way with, or assist or
         participate in, facilitate or encourage, any effort or attempt by any
         other person to do or seek to do any of the foregoing;

PROVIDED, that this Section 4.4 shall not prohibit (i) the Company from (A)
furnishing to any person that has made an unsolicited, bona fide written
proposal with respect to an Alternative Transaction information concerning the
Company and its subsidiaries and the business, properties, operations, prospects
or condition (financial or otherwise) of the Company and its subsidiaries or (B)
engaging in discussions or negotiations with such person that has made such
written proposal with respect to an Alternative Transaction, (ii) following
receipt of such written proposal with respect to an Alternative Transaction, the
Company from taking and disclosing to its stockholders a position contemplated
by Rule 14e-2(a) under the Exchange Act, (iii) following receipt of such written
proposal with respect to an Alternative Transaction, the Board from withdrawing
or modifying the Board's approval of the Stock Purchase, or (iv) the Board from
recommending that the stockholders of the Company accept and approve such
proposal with respect to an Alternative Transaction or authorizing, recommending
or proposing an agreement with respect to such written proposal; PROVIDED,
HOWEVER, that the Company or the Board, as the case may be, shall (w) take any
action referred to in the preceding clause (iv) only after the Company gives the
Purchasers two business days advance notice of its intention to take any such
action, (x) take any action referred to in the preceding clauses (i), (iii) and
(iv) above only after the Board (after having consulted with its financial
advisors) concludes in good faith that any proposed Alternative Transaction
referred to in such clauses offers terms more favorable to the Company and its
stockholders from a financial point of view than the Investment (including
arrangements under the Commercial Agreements), taking into account (A) the terms
and conditions of the proposed Alternative Transaction and this Agreement
(including the other Transaction Documents and the Commercial Agreements),
respectively, (B) all other legal,
<PAGE>
                                                                 Page 165 of 229

financial, regulatory and other aspects of such proposed Alternative Transaction
and the Investment (including arrangements under the Commercial Agreements), (C)
the identity of the person proposing such Alternative Transaction, (D) the
Board's determination of whether such proposed Alternative Transaction is
reasonably capable of being completed and (E) whether financing for such
proposed Alternative Transaction, to the extent required, as reasonably
determined by the Board of Directors, will be available (an Alternative
Transaction meeting the forgoing criteria on its most recently amended or
modified terms, if amended or modified, a "Superior Proposal"), and only if in
the good faith opinion of the Board (based upon an opinion of the Company's
outside counsel) to do so is required in the exercise of the directors'
fiduciary duties and (y) furnish to the person making such Superior Proposal any
information referred to in the preceding clause (i) only if both (A) the Company
then promptly furnishes such information to the Purchasers, or shall have
previously furnished such information to the Purchasers, and (B) such
information shall be so furnished to such person pursuant to a confidentiality
agreement no less favorable to the Company then the terms of the Confidentiality
Agreement referred to in Section 4.6 and (z) shall take any action referred to
in the preceding clauses (i), (ii) and (iii) only if the Board of Directors of
the Company shall promptly thereafter, by written notice delivered to the
Purchasers, inform the Purchasers of its intention to take such action. The
Company will promptly notify the Purchasers if any person makes any proposal,
offer, inquiry, or contact with respect to any of the foregoing. The Company
shall cease and cause to be terminated any existing activities, discussions or
negotiations with all persons (other than the Purchasers or any affiliate of, or
any person acting in concert with, the Purchasers) conducted on or before the
date of this Agreement with respect to any Alternative Transaction. The Company
shall inform the persons referred to in the first sentence of this Section 4.4
of the obligations undertaken by it in this Section 4.4.

         Section 4.5 ACCESS TO INFORMATION. Upon reasonable notice and subject
to restrictions contained in confidentiality agreements to which such party is
subject (from which such party shall use reasonable efforts to be released), the
Company shall (and shall cause each of its subsidiaries to) afford to the
officers, employees, accountants, counsel and other representatives of the
Purchasers, reasonable access, during the period from the date hereof until the
Closing Date, to all of its properties, books, contracts, commitments and
records and, during such period, the Company shall (and shall cause each of its
subsidiaries to) furnish promptly to the Purchasers and the officers, employees,
accountants, counsel and other representatives of the Purchasers, all
information concerning its business, properties and personnel as the Purchasers
may reasonably request, and shall make available to the Purchasers the
appropriate individuals (including attorneys, accountants and other
professionals) for discussion of the Company's business, properties and
personnel as the Purchasers may reasonably request. Each party shall keep such
information confidential in accordance with the terms of Section 4.6 hereof.

         Section 4.6 CONFIDENTIALITY. It is understood by each of the Purchasers
that the information, documents and instruments delivered to such Purchaser
directly or indirectly by the Company or its agents and the information,
documents and instruments delivered to the Company by the Purchasers or their
respective agents are of a confidential and proprietary nature (the
"confidential information"). Each of the parties hereto agrees that both prior
and
<PAGE>
                                                                 Page 166 of 229

subsequent to the Closing it will maintain the confidentiality of all such
confidential information delivered to it by each of the other parties hereto or
their agents in connection with the negotiation of this Agreement or in
compliance with the terms, conditions and covenants hereof and will only
disclose such confidential information to its duly authorized officers,
partners, directors, representatives and agents. The term "confidential
information" does not include any information that (i) at the time of disclosure
or thereafter is generally available to and known by the public (other than as a
result of its disclosure directly or indirectly by a Purchaser or one of its
agents), (ii) was available to such Purchaser on a non-confidential basis from a
source other than the Company or its advisors, provided that such source is not
and was not bound by a confidentiality agreement regarding the Company, or (iii)
has been independently acquired or developed by such Purchaser without violation
of any obligations under this section. Each of the parties hereto further agrees
that if the transactions contemplated hereby are not consummated, it will return
all such documents and instruments and all copies thereof in its possession to
the other party to this Agreement. Each of the parties hereto recognizes that
any breach of this Section 4.6 would result in irreparable harm to the other
parties to this Agreement and their affiliates and that therefore either the
Company or the Purchasers, as the case may be, shall be entitled to seek an
injunction to prohibit any such breach or anticipated breach, without the
necessity of posting a bond, cash or otherwise, in addition to all of their
other legal and equitable remedies. Nothing in this Section 4.6, however, shall
prohibit the use of such confidential information as in the opinion of the
Company's counsel or any Purchaser's counsel are required by law or governmental
regulations or judicial process; provided, however, that no such disclosure
shall be made without reasonable notice to the party that is the source of such
confidential information.

         Section 4.7 CONSENTS; APPROVALS. The Company shall use commercially
reasonable efforts to obtain all consents, waivers, approvals, authorizations or
orders required in connection with the execution of this Agreement and the
consummation of the transactions contemplated hereby (including, without
limitation, (i) consents under the agreements set forth on Section 4.7 of the
Company's Disclosure Schedule and (ii) all United States and foreign
governmental and regulatory rulings and approvals), and the Company shall make
all filings (including, without limitation, all filings with United States and
foreign governmental or regulatory agencies) required in connection with the
authorization, execution and delivery of this Agreement by the Company and the
consummation by it of the transactions contemplated hereby, in each case as
promptly as practicable. The Company and the Purchasers shall furnish promptly
all information required to be included in the Proxy Statement or for any
application or other filing to be made pursuant to the rules and regulations of
any United States or foreign governmental body in connection with the
transactions contemplated by this Agreement. The Company also shall use
commercially reasonable efforts to obtain all necessary permits and approvals
required under applicable Blue Sky Laws to carry out the transactions
contemplated hereby and shall furnish all information as may be reasonably
requested in connection with any such action. Nothing in this Section 4.6 or any
other provision of any Transaction Document shall require any Purchaser to sell
or otherwise dispose of any substantial amount of the assets of any of the
Purchasers and
<PAGE>
                                                                 Page 167 of 229

their respective subsidiaries, whether as a condition to obtaining any consent,
waiver, approval, authorization or order from a Governmental Body or any other
person or for any other reason.

         Section 4.8 PUBLIC ANNOUNCEMENTS. The Purchasers and the Company shall
consult with each other before issuing any press release or public statement or
making any filing with respect to the Stock Purchase or this Agreement and shall
not issue any such press release or make any such public statement or filing
without the prior consent of the other party, which consent shall not be
unreasonably withheld; PROVIDED, HOWEVER, that a party may, without the prior
consent of the other party, issue such press release or make such public
statement or filing as may upon the advice of counsel be required by law or the
rules and regulations of the Nasdaq National Market ("NASDAQ"), if it has used
all reasonable efforts to consult with the other party prior thereto, and shall
promptly notify the other parties hereto thereof.

         Section 4.9 LISTING. The Company shall use its best efforts to (i)
continue the quotation of its Common Stock on the Nasdaq during the term of this
Agreement and for so long as any of the Shares are outstanding and (ii) to file
all forms, accompanied by the appropriate fee, to include the shares of Common
Stock into which the Shares are convertible and for which the Warrants may be
exercisable, in the Common Stock listed for quotation.

         Section 4.10 BOARD OF DIRECTORS. The Certificate of Designation
provides for up to two directors to be elected by class vote of the holders of
Preferred Stock. For so long as the Purchasers or their permitted assignees have
a right under the Certificate of Designation to elect one or more directors,
this Section 4.10 shall govern the mechanism of their election, and is to
operate in conformity with, rather than in addition to, the Certificate of
Designation. At such time as such provisions in the Certificate of Designation
no longer apply, the provisions of this Section 4.10 shall determine the
Company's obligations with regard to the nomination of directors representing
the Purchasers.

              (a) On the day after the Closing Date the Company shall take all
         necessary action to elect two nominees of the Purchasers to the
         Company's Board as provided in the Certificate of Designation. No later
         than the Closing Date, each of U.S. Telesource, Inc. ("TELESOURCE") and
         Oak shall provide to the Company one nominee's name (the "TELESOURCE
         NOMINEE" and the "OAK NOMINEE", respectively, and together the
         "NOMINEES") as soon as practicable after the Closing. The Telesource
         Nominee shall be elected to the class of directors whose current term
         expires in 2000 (the "CLASS II") and the Oak Nominee shall be elected
         to the class of directors whose current term expires in 2001 ("CLASS
         I").

              (b) The Company agrees to take the following action regarding
         ongoing representation on the Board of Directors:

                           (i) Until the date that Telesource and its affiliates
                  no longer own a number of shares of Preferred Stock and Common
                  Stock greater than or equal to one-quarter of the number of
                  shares of Preferred Stock issued to Telesource on the
<PAGE>
                                                                 Page 168 of 229

                  Closing Date (or Common Stock into which such Preferred Stock
                  was convertible), Telesource will have the right to nominate
                  the Telesource Nominee for a Class II director upon each
                  regular election of such class of directors. Such number of
                  shares shall be appropriately adjusted to reflect stock
                  splits, dividends, recapitalizations and the like.

                           (ii) Until the date that Oak, MeriTech, Accel,
                  Brentwood, Worldview, Bessemer Venture Partners IV, L.P. and
                  Adams Capital Management, L.P. together no longer own a number
                  of shares of Preferred Stock and Common Stock greater than or
                  equal to one-quarter of the number of shares of Preferred
                  Stock issued to all of them on the Closing Date (or Common
                  Stock into which such Preferred Stock was convertible), Oak
                  will have the right to nominate the Oak Nominee for a Class I
                  director upon each regular election of such class of
                  directors. Such number of shares shall be appropriately
                  adjusted to reflect stock splits, dividends, recapitalizations
                  and the like.

                           (iii) In the event that the right of the holders of
                  Preferred Stock to elect two directors pursuant to Section
                  4(d) of the Certificate of Designation shall terminate, the
                  Purchasers shall designate whichever Nominee is in the class
                  of directors to be elected at the next meeting of
                  stockholders, or if neither Nominee is in such class, then in
                  the next-subsequent class, as the director as to whom a class
                  vote of the Preferred Stock is required. The other Nominee
                  shall then continue in accordance with the Company's by-laws,
                  and the provisions of this Section 4.10 shall control the
                  re-election or replacement of such Nominee. In the event that
                  holders of Preferred Stock have no right to elect any
                  directors pursuant to the Certificate of Designation, this
                  Section 4.10 shall govern the nomination of the Nominees.

                           (iv) Each of Telesource and Oak shall notify the
                  Company in writing of the identity of its Nominee, as
                  applicable, for election to the Board at the same time
                  shareholder proposals are due as set forth in the Company's
                  proxy statement filed the preceding year for an election year
                  when either of them has such a right, which notice shall be
                  conclusive evidence of the consent of such nominee to serve as
                  a director of the Company. In the event either Telesource or
                  Oak fails to provide such notice, the then-serving Telesource
                  Nominee or Oak Nominee, as applicable, for the class of
                  directors being elected shall be deemed to be renominated. The
                  notice shall include all information with respect to such
                  nominee as is required to be included in a proxy statement
                  soliciting proxies for the election of directors pursuant to
                  Regulation 14A of the Exchange Act. In the event of any
                  vacancy arising by reason of the resignation, death, removal
                  or inability to serve of the Telesource Nominee or the Oak
                  Nominee, Telesource or Oak, as applicable, shall notify the
                  Company of its choice to fill such vacancy, and the Company
                  shall take all actions necessary to elect such person to serve
<PAGE>
                                                                 Page 169 of 229

                  until the next meeting of the stockholders for the election of
                  directors of the Company.

                           (v) In any year when either Telesource or Oak has
                  such a right, the Company shall cause the Telesource Nominee
                  or the Oak Nominee, as applicable, nominated by Telesource or
                  Oak for election to the Board to be included in the slate of
                  nominees presented by the Board to the stockholders of the
                  Company for election as directors at the relevant annual
                  meeting of the stockholders, and shall use its reasonable
                  efforts to cause the election of such Telesource Nominee or
                  Oak Nominee, as applicable, including soliciting proxies in
                  favor of the election of such nominee. The Company shall not
                  solicit proxies of the stockholders of the Company to vote
                  against any such nominee or for the approval of any
                  stockholder or other proposals that are inconsistent with the
                  rights afforded the Purchasers pursuant to this Section 4.10.

                           (vi) For so long as the Purchasers' have such a
                  right, the Company shall use its best efforts at all times to
                  take such action as is necessary to ensure that the Board
                  nominates and presents to stockholders the proposed election
                  of the Telesource Nominee or the Oak Nominee, as applicable.
                  As a condition precedent to the inclusion of any proposed
                  nominee to be presented to stockholders by the Board pursuant
                  to this Section 4.10, the Board or, if established, the
                  nominating committee of the Board, may review the information
                  provided pursuant to this Section 4.10 to evaluate in good
                  faith such nominee's character and fitness to serve as a
                  director. If the Board or the nominating committee, as the
                  case may be, determines in good faith that any such nominee
                  lacks the character or fitness to serve as a director based on
                  applicable legal and reasonable commercial standards, the
                  Board or the nominating committee, as the case may be, shall
                  inform Telesource or Oak, as applicable, of such
                  determination, and Telesource or Oak, as applicable, shall
                  then have the right to propose an alternative nominee.

                           (vii) For so long as the Purchasers have the right to
                  nominate nominees for election to the Board as set forth in
                  this Section 4.10, any committee of the Board shall include at
                  least one of the Purchaser Nominees (except for any committee
                  on which neither of them is eligible to serve under the Nasdaq
                  listing rules).

         Section 4.11 CERTIFICATE OF DESIGNATION. The Company shall, prior to
the Closing, cause to be filed with the Secretary of State of Delaware, a
certificate of designation in the form attached hereto as EXHIBIT C,
establishing the terms and conditions of the Preferred Stock (the "CERTIFICATE
OF DESIGNATION").

         Section 4.12 INCREASE OF OPTION POOL. The Company shall submit for
stockholder approval at the Stockholders Meeting a proposal to approve a 4
million share increase in the
<PAGE>
                                                                 Page 170 of 229

number of shares of Common Stock issuable pursuant to the Company's Restated
Equity Incentive Plan. Section 1.1

         Section 4.13 USE OF PROCEEDS. The proceeds received by the Company from
the issuance of the Notes will be used in accordance with the provisions of
Section 4.14 hereof, and the proceeds from the sale of the Shares shall be used
by the Company in the furtherance of the business plan approved by the Board of
Directors on May , 1999, as such plan may be amended by the Board following the
Closing (the "BUSINESS STRATEGY PLAN").

         Section 4.14 INTERIM OPERATIONS. The Company covenants and agrees that
during the period from the date of this Agreement and until the earlier of the
termination of this Agreement pursuant to Section 6.1 or the Closing, unless the
Company and Two-Thirds in Interest of the Purchasers otherwise prior thereto
agree, each of the Company and its subsidiaries shall conduct its business in
the ordinary course in the three markets, two pilot programs and facility update
programs listed on Schedule 4.14 or in furtherance of the Business Plan as it
relates to the period prior to commencement of revenue operations thereunder and
shall not, except either as contemplated by this Agreement or in furtherance of
the Business Strategy Plan, do any of the following: (i) except for any payments
required to obtain consents required to be obtained pursuant to this Agreement,
incur, assume or guarantee any liability or pay, discharge or satisfy any
liability other than in the ordinary course of business; (ii) create or assume
any Lien other than in the ordinary course of business; (iii) waive, release,
cancel, settle or compromise any debt, claim or right of any material value;
(iv) transfer or waive any material right under any material lease, license or
agreement or any material Company Intellectual Property; (v) pay or agree to pay
any bonus, extra compensation, pension, continuation, severance or termination
pay, or otherwise increase the wage, salary, pension, continuation, severance or
termination pay or other compensation (of any nature) to its directors, officers
or employees, except as required by law, other than for normal compensation
increases and promotions for employees (other than for executive officers) in
the ordinary course of business, as provided in the Company's plans and
agreements identified in the Disclosure Schedule or as are not material in the
aggregate; (vi) make any loan to or enter into any transaction with any of its
directors, officers or employees (other than pursuant to any such person's
status as an employee of the Company) giving rise to any claim or right of, by,
or against any person in an amount or having a value in excess of $10,000
individually, except travel and entertainment advances in the ordinary course of
business and consistent with Company policies; (vii) enter into, amend or
terminate any material agreement or transaction; (viii) make any contribution to
any Employee Plan, other than regularly scheduled contributions and
contributions required to maintain the funding levels of any Employee Plan, or
make or incur any commitment to establish or increase the obligation of the
Company or a subsidiary to any Employee Plan; (ix) create, assume or incur any
indebtedness for money borrowed, or guaranties thereof, except for trade
accounts payable incurred in the ordinary course of business or borrowings under
the Company's working capital line of credit facility as in effect on the date
hereof, or issue any debt securities, warrants or other rights to acquire any
debt securities of the Company or any of its subsidiaries; (x) issue, deliver or
sell, or authorize or propose the issuance, delivery or sale of, any shares of
capital stock of any class, any securities convertible into or exercisable for,
or any rights, warrants or options to
<PAGE>
                                                                 Page 171 of 229

acquire, any such shares, of the Company or any of its subsidiaries except for
(A) the grant of options to acquire not more than 100,000 shares in the
aggregate to new employees or promoted employees (other than executive officers)
in the ordinary course of business pursuant to its equity incentive plans or
automatic grants of options and deferred stock pursuant to the director's equity
incentive plan, in each case as in effect on the date hereof or (B) stock issued
upon exercise of outstanding options and warrants; (xi) amend or modify any
provision of the Business Strategy Plan; (xii) amend or modify any provision of
its charter, by-laws or other governing documents, except for the proposed
amendments to the Company's by-laws set forth on Schedule 2.8; (xiii) make any
capital expenditures for capital improvements or commitments therefor except as
committed on the date hereof and in any event limited in the aggregate to
$6,200,000; (xiv) expand the Company's network or operations beyond its three
existing markets, two pilot programs and facility update program or expand its
marketing beyond its three existing markets; (xv) sell, assign or dispose of any
of the FCC Licenses listed on Exhibit 2.19 or any right thereunder; or (xvi)
agree to or make any commitment to take any actions prohibited by this Section
4.14.

         Section 4.15 RESTRICTED SECURITIES. Each Purchaser understands that the
Shares purchased by it and the Common Stock issued upon conversion thereof
(collectively the "SECURITIES") may not be sold, transferred, or otherwise
disposed of without registration under the Securities Act, or an exemption
therefrom, and that in the absence of an effective registration statement
covering such Securities or an available exemption from registration under the
Securities Act, such Securities must be held indefinitely. Each Purchaser agrees
not to make any disposition of all or any portion of the Securities unless and
until:

                  (1) There is then in effect a registration statement under the
         Securities Act covering such proposed disposition and such disposition
         is made in accordance with such registration statement and all
         applicable Blue Sky Laws; or

                  (2) (A) Such Purchaser shall have notified the Company of the
         proposed disposition and (B) such Purchaser shall have furnished the
         Company with an opinion from counsel, reasonably satisfactory to the
         Company, that such disposition will not require registration of such
         shares under the Securities Act and any applicable Blue Sky Laws in
         connection with such disposition.

         Notwithstanding the provisions of paragraphs (1) and (2) above, no such
registration statement or opinion of counsel shall be necessary for a transfer
by any Purchaser with or without consideration to a partner, member, subsidiary,
shareholder or affiliate of such Purchaser, including, without limitation, any
partner of such Purchaser and any venture capital fund now or hereafter existing
which is controlled by or is under common control with one or more general
partners of such Purchaser, provided such transferee becomes a party to this
Agreement and specifically agrees to be bound by the agreement in this Section
4.15.

         Section 4.16 PREEMPTIVE RIGHTS.
<PAGE>
                                                                 Page 172 of 229

              (a) Subject to the provisions of Section 4.16 (c), in the event
         that following the Closing, the Company proposes to raise additional
         capital through the issuance of Common Stock (or securities convertible
         into or exercisable or exchangeable for Common Stock) other than an
         issuance of Excluded Securities ("New Securities"), each Purchaser
         shall have the right to purchase equity of such type and on
         substantially the same economic terms, including purchasing other
         securities issued by the Company, as the Company issues or sells, such
         that the Purchaser shall have the opportunity to maintain its then
         fully-diluted equity ownership percentage in the Company, subject to
         and in accordance with the provisions of Sections 4.16 (b). The then
         fully-diluted equity ownership percentage of each Purchaser (such
         Purchaser's "Purchaser Percentage") shall be the quotient of (i) the
         sum of the number of shares of Common Stock then held by such Purchaser
         plus the number of shares of Common Stock issuable upon conversion of
         any Shares then held by such Purchaser plus the number of shares of
         Common Stock then held by such Purchaser issued to such Purchaser as
         New Securities, or issuable upon exercise or conversion of New
         Securities issued to such Purchaser then held by such Purchaser divided
         by (ii) the total number of shares of Common Stock outstanding plus the
         number of shares of Common Stock issuable upon conversion of any Shares
         then outstanding plus the number of shares of Common Stork issuable
         upon the exercise or conversion of any security exercisable or
         exchangeable for or convertible into Common Stock.

              (b) The rights of the Purchaser under Section 4.16(a) shall be
         effected in accordance with the following:

                           (i) The Company shall give written notice to each
                  Purchaser as soon as practicable of its intention to issue New
                  Securities;

                           (ii) The Company shall supply each Purchaser with
                  copies of all relevant documents relating to such issuance as
                  are provided to potential purchasers in such an issuance at
                  substantially the same time as provided to such potential
                  purchasers;

                           (iii) The Company shall inform potential purchasers
                  of such New Securities of the rights of the Purchasers under
                  this Section 4.16 to subscribe for a portion of such issuance.
                  Each Purchaser shall make a good faith effort to provide the
                  Company with an estimate of its intent to exercise its rights
                  under this Section 4.16 before the Company distributes final
                  documents to potential purchasers of the New Securities;

                           (iv) The Company shall provide each Purchaser with
                  copies of all of the executed agreements relating to each such
                  issuance; and

<PAGE>
                                                                 Page 173 of 229

                           (v) Within ten days following each Purchaser's
                  receipt of agreements pursuant to (iv) above, such Purchaser
                  shall provide written notice to the Company (the "Commitment
                  Notice") as to whether such Purchaser exercises its rights
                  under this Section 4.16 with respect to such issuance, and, if
                  so, the number of securities to be purchased by such
                  Purchaser. If any Purchaser fails to provide the Commitment
                  Notice within the stated ten day period, such Purchaser will
                  be deemed to have waived its rights under Section 4.16 of this
                  Agreement with respect to such issuance. The Commitment Notice
                  of each Purchaser shall constitute a binding and enforceable
                  commitment by such Purchaser subject to any closing conditions
                  contained in the agreements referred to in clause (iv) above,
                  to purchase the lower of (a) number of securities specified in
                  such Purchaser's Commitment Notice and (b) such Purchaser's
                  Purchaser Percentage of the number of securities sold in such
                  issuance at the price and on all of the other terms and
                  conditions of such issuance (including, if appropriate,
                  signing the same documents as signed by other purchasers)
                  either (i) if such issuance has not yet been consummated, at
                  the same time as such securities are sold or (ii) if such
                  issuance has been consummated, within twenty days of the date
                  of the receipt by Purchaser of the agreements pursuant to (iv)
                  above.

              (c) The rights of each Purchaser under this Section 4.16 shall
         terminate on the first date on which such Purchaser no longer holds
         Common Stock or Preferred Stock representing at least 25% of the Common
         Stock into which the Shares purchased by such Purchaser hereunder are
         ultimately convertible (determined on an as if fully converted basis).

              (d) "Excluded Securities" shall mean (i) any securities issued
         pursuant to any Company equity incentive plan or benefit plan or, (ii)
         any securities issued in connection with any stock split, stock
         dividend or other similar event, (iii) any securities issued pursuant
         to the Rights Plan, (iv) any security issued upon exercise, conversion
         or exchange of any New Security, Excluded Security or security
         outstanding on the date hereof, (v) any issuance of securities in a
         private placement in an offering customarily known as a "144A Offering"
         in which either the investors have the right to exchange any purchased
         securities for securities registered under the Securities Act or a
         similar right to cause the registration of or otherwise freely trade
         such securities, (vi) any issuance of securities issued to financial
         institutions or other lenders in connection with any offering of debt
         securities or borrowing by the Company, (vii) any issuance of
         securities in a public offering registered under the Securities Act,
         (viii) any issuance of securities as consideration for the acquisition
         of assets or any ownership interest in any Person, (ix) any conversion
         of the Preferred Stock and (x) any other securities deemed to be
         Excluded Securities by the Company and Two-Thirds in Interest of the
         Purchasers.

         Section 4.17 AMENDMENT OF RIGHTS AGREEMENT. Prior to the Closing, the
Company shall have amended the Rights Agreement in substantially the form
presented to the Purchasers on the date hereof.
<PAGE>
                                                                 Page 174 of 229

         Section 4.18 FCC APPROVALS. The Company covenants and agrees that
within ninety (90) days following the Closing, the Company shall file and use
commercially reasonable efforts to obtain a grant of substantive transfer of
control applications with the FCC detailing the new ownership of the Company to
avoid regulatory delays for future conversion of convertible instruments.


                                   ARTICLE V.

                        CONDITIONS TO THE STOCK PURCHASE

         Section 5.1 CONDITIONS TO OBLIGATION OF EACH PARTY TO EFFECT THE STOCK
PURCHASE. The respective obligations of each party to effect the Stock Purchase
shall be subject to the satisfaction at or prior to the Closing Date of the
following conditions:

              (a) STOCKHOLDER APPROVAL. The Stock Purchase shall have been
         approved by the holders of at least a majority of the votes cast at the
         Special Meeting, provided that a quorum shall be present;

              (b) HSR ACT. All waiting periods applicable to the consummation of
         the Stock Purchase under the HSR Act shall have expired or been
         terminated; and

              (c) NO INJUNCTIONS OR RESTRAINTS; ILLEGALITY. No temporary
         restraining order, preliminary or permanent injunction or other order
         issued by any court of competent jurisdiction or other legal restraint
         or prohibition preventing the consummation of the Stock Purchase shall
         be in effect, nor shall any proceeding brought by any administrative
         agency or commission or other governmental authority or
         instrumentality, domestic or foreign, seeking any of the foregoing be
         pending; and there shall not be any action taken, or any statute, rule,
         regulation or order enacted, entered, enforced or deemed applicable to
         the Stock Purchase, which makes the consummation of the Stock Purchase
         illegal.

         Section 5.2 ADDITIONAL CONDITIONS TO OBLIGATIONS OF THE PURCHASERS. The
obligations of the Purchasers to effect the Stock Purchase are also subject to
the following conditions:

              (a) REPRESENTATIONS AND WARRANTIES. The representations and
         warranties of the Company contained herein shall be true and correct
         (as if any materiality qualifications were not contained therein) at
         and as of the Closing Date as if made at and as of such date, except
         for (i) changes contemplated by this Agreement, (ii) those
         representations and warranties which address matters only as of a
         particular date (which shall have been true and correct as of such
         date) and (iii) where the failure to be true and correct does not
         constitute a Material Adverse Effect, with the same force and effect as
         if made at and as of the Closing Date and the Purchasers shall have
         received a certificate to such effect
<PAGE>
                                                                 Page 175 of 229

         signed on behalf of the Company by the Chairman, President or the Chief
         Financial Officer of the Company;

              (b) AGREEMENTS AND COVENANTS. The Company shall have performed or
         complied in all material respects with all agreements and covenants
         required by this Agreement to be performed or complied with by it at or
         prior to the Closing Date, and the Purchasers shall have received a
         certificate to such effect signed on behalf of the Company by the
         Chairman, President or Chief Financial Officer of the Company;

              (c) CONSENTS OBTAINED. All consents, waivers, approvals,
         authorizations or orders required to be obtained, and all filings
         required to be made, by the Company for the due authorization,
         execution and delivery of this Agreement and the consummation by it of
         the transactions contemplated hereby shall have been obtained and made
         by the Company, except where the failure to receive such consents,
         waivers, approvals, authorizations or orders could not reasonably be
         expected to (i) have a Material Adverse Effect on the Company, or (ii)
         significantly delay or prevent the consummation of the Stock Purchase;

              (d) AMENDMENT OF THE INDENTURE. The Company shall have obtained
         the consent of holders of not less than two-thirds in principal amount
         of the Company's senior notes issued pursuant to the Indenture dated as
         of February 6, 1997 between the Company and The Bank of New York, as
         Trustee (the "INDENTURE") to the valid and effective amendment of the
         Indenture pursuant to an instrument in substantially the form provided
         to the Purchasers on the date hereof, unless otherwise agreed to by the
         Company and Two-Thirds in Interest of the Purchasers;

              (e) OPINION OF COUNSEL. The Purchasers shall have received a
         written opinion from Ropes & Gray, in form and substance reasonably
         satisfactory to the Purchasers, substantially in the form of EXHIBIT D
         hereto;

              (f) FCC OPINION. The Purchasers shall have received a written
         opinion from Wiley, Rein & Fielding, the Company's FCC counsel, in form
         and substance reasonably satisfactory to the Purchasers, substantially
         in the form of EXHIBIT E hereto;

              (g) BLUE SKY LAWS. The Company shall have received all permits and
         other authorizations necessary under the Blue Sky Laws to issue the
         Shares and the Common Stock issuable upon conversion thereof pursuant
         to the Stock Purchase;

              (h) NASDAQ LISTING. The shares of Common Stock issuable upon
         conversion of the Shares shall have been listed or approved for listing
         upon notice of issuance on Nasdaq;
<PAGE>
                                                                 Page 176 of 229

              (i) REGISTRATION RIGHTS AGREEMENT. The Company shall have executed
         and delivered to the Purchasers the Registration Rights Agreement in
         substantially the form of EXHIBIT F hereto;

              (j) DELIVERY OF SHARES. The Company shall have delivered the
         Shares to be delivered pursuant to Section 1.2 hereof against the
         payment of the Purchase Price;

              (k) RESIGNATION OF DIRECTORS. Two current members of the Board
         shall have resigned immediately prior to Closing and there shall be one
         Class I vacancy and one Class II vacancy on the Board, to be filled in
         accordance with Section 4.10;

              (l) COMMERCIAL AGREEMENTS. The Company and Qwest Communications
         Corporation ("Qwest") shall have executed and delivered (i) the Qwest
         Communications Corporation Private Line Services Agreement between the
         Company and Qwest in the form of Exhibit G, (ii) the Collocation
         License Agreement between the Company and Qwest in the form of Exhibit
         H, and (iii) the Coordinated Marketing Agreement between the Company
         and Qwest in the form of Exhibit I (collectively, the "COMMERCIAL
         AGREEMENTS"); and

              (m) CORPORATE PROCEEDINGS. The Secretary or an Assistant Secretary
         of the Company shall have delivered to the Purchasers a certificate,
         dated as of the Closing, certifying to the Company's charter and
         bylaws, the incumbency and specimen signatures of its certain officers
         and the corporate action taken by the Company in connection with the
         Transaction Documents.

         Section 5.3 ADDITIONAL CONDITIONS TO OBLIGATION OF THE COMPANY. The
obligation of the Company to effect the Stock Purchase is also subject to the
following conditions:

              (a) REPRESENTATIONS AND WARRANTIES. The representations and
         warranties of the Purchasers contained in this Agreement shall be true
         and correct in all material respects on and as of the Closing Date,
         except for (i) changes contemplated by this Agreement and (ii) those
         representations and warranties which address matters only as of a
         particular date (which shall have been true and correct as of such
         date), with the same force and effect as if made on and as of the
         Closing Date, and the Company shall have received a certificate to such
         effect signed by the President or Chief Financial Officer of each
         Purchaser or of the general partner of each of the Purchasers, as
         applicable;

              (b) AGREEMENTS AND COVENANTS. The Purchasers shall have performed
         or complied in all material respects with all agreements and covenants
         required by this Agreement to be performed or complied with by them on
         or prior to the Closing Date, and the Company shall have received a
         certificate to such effect signed by the President or Chief Financial
         Officer of the general partner or manager of each of the Purchasers;
<PAGE>
                                                                 Page 177 of 229

              (c) CONSENTS OBTAINED. All consents, waivers, approvals,
         authorizations or orders required to be obtained, and all filings
         required to be made, by the Company for the due authorization,
         execution and delivery of this Agreement and the consummation by it of
         the transactions contemplated hereby shall have been obtained and made
         by the Company, except where the failure to receive such consents,
         waivers, approvals, authorizations or orders could not reasonably be
         expected to (i) have a Material Adverse Effect on the Company, or (ii)
         significantly delay or prevent the consummation of the Stock Purchase;
         PROVIDED, that the Company will be deemed to have waived this condition
         if the failure to obtain such consents and waivers is due to the
         Company's material breach of its obligations under this Agreement;

              (d) PAYMENT OF PURCHASE PRICE. Each of the Purchasers shall have
         delivered full payment of the Purchase Price for the Shares to be
         purchased by such Purchaser at the Closing as set forth on Schedule I
         hereof.

              (e) STANDSTILL AGREEMENT. The Standstill Agreement in the form of
         Exhibit K shall have been duly executed and delivered by each of the
         Purchasers party thereto and shall be in full force and effect and
         shall not have been breached in any material respect by any of such
         Purchasers.

              (f) COMMERCIAL AGREEMENTS. The Company and Qwest shall have
         executed and delivered each of the Commercial Agreements.


                                  ARTICLE VI.

                                   TERMINATION

         Section 6.1 TERMINATION. This Agreement may be terminated at any time
prior to the Closing Date, notwithstanding approval thereof by the stockholders
of the Company:

              (a) by mutual written consent of the Company and Two-Thirds in
         Interest of the Purchasers; or

              (b) by either Two-Thirds in Interest of the Purchasers or the
         Company if a court of competent jurisdiction or governmental,
         regulatory or administrative agency or commission shall have issued a
         nonappealable final order, decree or ruling or taken any other action
         having the effect of permanently restraining, enjoining or otherwise
         prohibiting the Stock Purchase; or

              (c) by Two-Thirds in Interest of the Purchasers, if the requisite
         vote of the stockholders of the Company shall not have been obtained by
         the Final Maturity Date (provided that the right to terminate this
         Agreement under this Section 6.1(c) shall not be
<PAGE>
                                                                 Page 178 of 229

         available to the Purchasers to the extent that their failure to provide
         information required to be included in the proxy statement has been the
         cause of or resulted in the failure to obtain the requisite stockholder
         vote on or before such date); or

              (d) by Two-Thirds in Interest of the Purchasers or the Company,
         (i) if any representation or warranty of the Company or the Purchasers,
         respectively, set forth in this Agreement shall be untrue when made, or
         (ii) upon a breach of any covenant or agreement on the part of the
         Company or the Purchasers set forth in this Agreement, such that the
         conditions set forth in Sections 5.2(a), 5.2(b), 5.3(a) or 5.3(b), as
         the case may be, would not be satisfied, provided that if any of the
         circumstances set forth in clause (i) or (ii) is curable within
         forty-five calendar days after notice of the Company's or the
         Purchasers', as the case may be, intent to terminate this Agreement,
         through the exercise of reasonable efforts and for so long as the
         Company or the Purchasers, as the case may be, continues to exercise
         such reasonable efforts, neither the Purchasers nor the Company, as the
         case may be, may terminate this Agreement under this Section 6.1(d)
         until after the last day of such period; or

              (e) by Two-Thirds in Interest of the Purchasers, if the Company or
         the Board shall have (A) authorized or recommended (or publicly
         announced its intention to authorize or recommend) an agreement with
         respect to an Alternative Transaction with respect to any of the
         Company and its subsidiaries, (B) recommended that the stockholders of
         the Company accept or approve any such Alternative Transaction or (C)
         modified or amended the approval by the Board of the Stock Purchase,
         including any modification or rescission of the adoption of resolutions
         covering the matters addressed in Section 2.4(b) and Section 4.17, in
         any respect materially adverse to the Purchasers or withdrawn such
         Board approval or authorized or recommended opposing the transaction;
         PROVIDED that (x) a communication of the Company to the Purchasers that
         advises that the Company has received a proposal with respect to an
         Alternative Transaction and that takes no position with respect to such
         proposal shall not be deemed to be a modification, amendment or
         withdrawal of the Board's approval of the Stock Purchase and (y) a
         "stop-look-and-listen" communication of the nature contemplated in Rule
         14d-9(e) under the Exchange Act with respect to an unsolicited tender
         offer or exchange offer that, if concluded in accordance with the terms
         thereof, would constitute or result in an Alternative Transaction with
         respect to any of the Company and its subsidiaries (other than the
         Stock Purchase), without more, shall not be deemed to be a
         modification, amendment or withdrawal of the Board's approval of the
         Stock Purchase if, within the time period contemplated by Rule 14e-2
         under the Exchange Act, the Board shall publicly confirm its approval
         of the Stock Purchase and recommend against the acceptance of such
         tender offer or exchange offer by the stockholders of the Company; or

              (f) by the Company, if (A) the Board of Directors of the Company
         shall have determined that an unsolicited, bona fide proposal made by
         any person with respect to an
<PAGE>
                                                                 Page 179 of 229

         Alternative Transaction with respect to the Company is a Superior
         Proposal, (B) the Board of Directors of the Company shall have complied
         in all material respects with Section 4.4 with respect to actions taken
         or proposed to be taken by the Company or the Board of Directors of the
         Company with respect to such Superior Proposal, (C) the Company shall
         have notified the Purchasers in writing, not less than two business
         days in advance of taking such action, of its election to terminate the
         obligations of the parties pursuant to this Section 6.1(f) for the
         purpose of recommending that the stockholders of the Company accept or
         approve such Superior Proposal or authorizing, recommending or
         proposing an agreement with respect to such Superior Proposal, (D) the
         Company and its advisors and representatives shall have discussed with
         the Purchasers during such two day period the modifications to the
         terms of this Agreement, the Transaction Documents and the Commercial
         Agreements that would permit the Company to conclude the Investment in
         lieu of concluding such Superior Proposal, and (E) at the end of such
         two business day period the Board of Directors of the Company shall
         have determined that such Superior Proposal continues to constitute a
         Superior Proposal; or

              (g) by the Company or Two-Thirds in Interest of the Purchasers, if
         the Closing has not occurred by the end of the second business day
         following the Final Maturity Date (provided that the right to terminate
         this Agreement under this Section 6.1(g) shall not be available to any
         party whose material breach of any representation or warranty or
         failure to fulfill any obligation under this Agreement has been the
         cause of or resulted in the failure of the Closing to occur on or
         before such date).

         Section 6.2 EFFECT OF TERMINATION. In the event of the termination of
this Agreement pursuant to Section 6.1, this Agreement shall forthwith become
void and there shall be no liability on the part of any party hereto or any of
its affiliates, directors, officers or stockholders except (i) as set forth in
Section 6.3 and Section 7.1 hereof, and (ii) nothing herein shall relieve any
party from liability for any breach hereof.

         Section 6.3 FEES AND EXPENSES. All fees and expenses incurred in
connection with this Agreement and the transactions contemplated hereby shall be
paid by the party incurring such expenses, whether or not the Stock Purchase is
consummated; provided that, the Company shall pay the reasonable fees (not to
exceed $150,000) and expenses of counsel to the Purchasers incurred in
connection with the negotiation, preparation, execution and delivery of this
Agreement and any other instruments and agreements contemplated hereby, and the
Company shall pay all fees incurred in connection with all required filings
under the HSR Act (not to exceed $180,000).
<PAGE>
                                                                 Page 180 of 229

                                  ARTICLE VII.

                               GENERAL PROVISIONS

         Section 7.1 EFFECTIVENESS OF REPRESENTATIONS, WARRANTIES AND
AGREEMENTS; KNOWLEDGE, ETC.

              (a) Except as otherwise provided in this Section 7.1, the
         representations, warranties and agreements of each party hereto shall
         remain operative and in full force and effect regardless of any
         investigation made by or on behalf of any other party hereto, any
         person controlling any such party or any of their officers or
         directors, whether prior to or after the execution of this Agreement.
         The representations, warranties and agreements in this Agreement and
         certificates delivered pursuant hereto shall survive the Closing Date
         until the date that is three months after the filing of the Company's
         Annual Report on Form 10-K for the period ended December 31, 1999 or
         upon the termination of this Agreement pursuant to Section 6.1, as the
         case may be, at which time they shall terminate and be of no further
         force or effect, except that the agreement set forth in Section 4.6
         shall survive for two years from the Closing Date, the agreements
         contained in Sections 4.10, 4.13, 4.15, 4.16, 7.1 or 7.2 shall last
         indefinitely, unless sooner terminated in accordance with their
         respective terms and the agreement set forth in Section 6.3 shall
         survive the Closing Date until paid.

              (b) Any disclosure made with reference to one or more sections of
         the Company Disclosure Schedule shall be deemed disclosed with respect
         to any section with such Disclosure Schedule to which such disclosure
         reasonably relates.

         Section 7.2 RESTRICTIVE LEGENDS. Each certificate representing Shares
or Conversion Shares shall bear legends in substantially the following form:

         The securities represented by this certificate have not been registered
         under the Securities Act of 1933 or the securities laws of any state
         and may not be sold or otherwise disposed of except pursuant to an
         effective registration statement under such Act and applicable state
         securities laws or an applicable exemption to the registration
         requirements of such Act or such laws.

         The securities represented by this certificate were issued pursuant to,
         and the holder hereof is entitled to certain rights and subject to
         certain obligations contained in, a Stock Purchase Agreement dated as
         of June __, 1999, a copy of which is available for inspection at the
         principal office of the issuer hereof, and will be furnished without
         charge to the holder of such securities upon written request.

         Each certificate representing Shares or Conversion Shares shall also
bear any other legends required by any applicable law.
<PAGE>
                                                                 Page 181 of 229

         Section 7.3 NOTICES. All notices and other communications given or made
pursuant hereto shall be in writing and shall be deemed to have been duly given
or made if and when delivered personally or by overnight courier to the parties
at the following addresses or sent by electronic transmission, with confirmation
received, to the telecopy numbers specified below (or at such other address or
telecopy number for a party as shall be specified by like notice):

                  (a) If to the Purchasers, to such address listed on Schedule I
         hereto, with a copy to:

                  Gunderson Dettmer Stough Villeneuve Franklin & Hachigian, LLP
                  155 Constitution Drive
                  Menlo Park, CA  94025
                  Attn:  Brooks Stough, Esq.
                  Telecopier No.:  (650) 321-2800
                  Telephone No.:  (650) 463-5370

         and to:
                  O'Melveny & Myers LLP
                  1999 Avenue of the Stars
                  Los Angeles, CA  90067-6035
                  Attn:  Steven L. Grossman, Esq.
                  Telecopier No.:  (310) 246-6779
                  Telephone No.:  (310) 553-6700


                  (b) If to the Company:

                  Advanced Radio Telecom Corp.
                  500 108th Avenue NE, Suite 2600
                  Bellevue, WA  98004
                  Attn: Thomas M. Walker, Esq., General Counsel
                  Telecopier No.: (425) 990-1642 or (425) 688-0703
                  Telephone No.:  (425) 990-1669

                  With a copy to:

                  Ropes & Gray
                  One International Place
                  Boston, MA  02110
                  Attn: Mary E. Weber, Esq.
                  Telecopier No.: (617) 951-7050
                  Telephone No.: (617) 951-7391
<PAGE>
                                                                 Page 182 of 229

         Section 7.4 CERTAIN DEFINITIONS. For purposes of this Agreement, the
term:

              (a) "AFFILIATE" means a person that directly or indirectly,
         through one or more intermediaries, controls, is controlled by, or is
         under common control with, the first mentioned person; including,
         without limitation, any partnership or joint venture in which the first
         mentioned person (either alone, or through or together with any other
         subsidiary) has, directly or indirectly, an interest of 10% or more;

              (b) "ALTERNATIVE TRANSACTION" means, whether concluded or intended
         to be concluded in any transaction or series of transactions, any of
         the following with respect to the Company and its subsidiaries (other
         than the transactions contemplated by this Agreement):

                           (1) the acquisition from the Company or from any
                           third persons of any equity securities of the Company
                           as a result of which the holders of equity securities
                           of the Company immediately before such transaction
                           would own beneficially directly or indirectly less
                           than 75% of the equity securities of the Company
                           issued and outstanding immediately after such
                           transaction;

                           (2) the merger or consolidation of any of the Company
                           with or into any person other than the Company or one
                           of its wholly-owned subsidiaries as a result of which
                           the holders of equity securities of the Company
                           immediately before such transaction would own
                           beneficially directly or indirectly less than 75% of
                           the equity securities of the Company or the surviving
                           entity issued and outstanding immediately after such
                           transaction;

                           (3) the sale of a substantial portion of the assets
                           of the Company and its subsidiaries to any person or
                           group other than the Company or its wholly-owned
                           subsidiaries; or

                           (4) any transaction (whether or not any of the
                           Company or its subsidiaries shall be a party thereto)
                           as a result of which a majority of the members of the
                           board of directors, or similar officials, of the
                           Company or such subsidiary would not be persons who
                           on the day after the closing date of such transaction
                           were members of the board of directors, or similar
                           officials, or who were nominated for election or
                           elected with the approval of a majority of the
                           directors, or similar officials, who were directors,
                           or similar officials, on that date or whose
                           nomination or election was previously so approved.
<PAGE>
                                                                 Page 183 of 229

              (c) "CONTROL" (including the terms "controlled by" and "under
         common control with") means the possession, directly or indirectly or
         as trustee or executor, of the power to direct or cause the direction
         of the management or policies of a person, whether through the
         ownership of stock, as trustee or executor, by contract or credit
         arrangement or otherwise;

              (d) "GOVERNMENTAL BODY" means any agency, bureau, commission,
         court, department, official, political subdivision, tribunal or other
         instrumentality of any government, whether federal, state, county or
         local, domestic or foreign, of competent jurisdiction.

              (e) "KNOWLEDGE" means the actual knowledge of any director or
         executive officer after reasonable investigation;

              (f) "MATERIAL ADVERSE EFFECT" means, when used in connection with
         the Company or any of the Company's subsidiaries, as the case may be,
         any change, effect or circumstance that, individually or when taken
         together with all changes, effects or circumstances that have occurred
         prior to the date of determination of the occurrence of the Material
         Adverse Effect and with respect to which such phrase is used, (a) has
         been, is or could reasonably be expected to be materially adverse to
         the business, assets, results of operations or condition (financial or
         otherwise) of the Company and its subsidiaries, in each case taken as a
         whole, or (b) is or is reasonably likely to delay or prevent the
         consummation of the transactions contemplated hereby.

              (g) "PERSON" means an individual, corporation, partnership,
         association, trust, unincorporated organization, other entity or group
         (as defined in Section 13(d)(3) of the Exchange Act).

              (h) "SUBSIDIARY" or "SUBSIDIARIES" of the Company or any other
         person means any corporation, partnership, joint venture or other legal
         entity of which the Company, or such other person, as the case may be
         (either alone or through or together with any other subsidiary), owns,
         directly or indirectly, more than 50% of the stock or other equity
         interests the holders of which are generally entitled to vote for the
         election of the board of directors or other governing body of such
         corporation or other legal entity.

              (i) "TWO-THIRDS IN INTEREST" means, prior to the Closing,
         Purchasers who have agreed to purchase more than 66-???% of the Shares
         and, on and after the Closing, Purchasers holding more than 66-???% of
         the Shares then owned by the Purchasers.

         Section 7.5 NOTIFICATION. The Company and each Purchaser agrees to give
prompt notice to the other parties to this Agreement or any other Transaction
Document, as the case may be, of (1) the occurrence, or failure to occur, of any
event that would be likely to cause any representation or warranty of the party
contained herein or therein to be untrue or inaccurate in any material respect
at any time from the date of this Agreement to the Closing Date, any failure
<PAGE>
                                                                 Page 184 of 229

of the party to perform or otherwise comply with, in any material respect, any
covenant, condition or agreement to be performed or complied with by it
hereunder or thereunder and (2) the receipt by the party of written or oral
notice from any Governmental Body or other person stating, or causing such party
to believe, that there is a reasonable likelihood that a consent, waiver,
approval, authorization or order required by this Agreement to be obtained from
such Governmental Body or other person will not be obtained timely or at all;
which covenant of notification shall not limit the right of any other party
hereunder or thereunder to require as a condition precedent to the performance
of its obligations hereunder or thereunder the continuing accuracy and
performance of the representations and warranties and covenants of the notifying
party made herein or therein and to receive an unqualified certificate with
respect to the same.

         Section 7.6 AMENDMENT. This Agreement may be amended upon the written
consent of the Company and Two-Thirds in Interest of the Purchasers, at any time
prior to the Closing Date, and such amendment shall be binding on all of the
Purchasers. This Agreement may not be amended except by an instrument in writing
signed by the Company and Two-Thirds in Interest of the Purchasers.

         Section 7.7 WAIVER. At any time prior to the Closing Date, the parties
hereto, upon the written consent of the Company and Two-Thirds in Interest of
the Purchasers, may (a) extend the time for the performance of any of the
obligations or other acts, (b) waive any inaccuracies in the representations and
warranties contained herein or in any document delivered pursuant hereto, or (c)
waive compliance with any of the agreements or conditions contained herein. Any
such waiver shall be binding on all of the Purchasers.

         Section 7.8 COOPERATION. Each Purchaser severally and the Company agree
to take, or to cause to be taken, all such reasonable and lawful action as may
be necessary to make effective and consummate the transactions contemplated by
this Agreement.

         Section 7.9 HEADINGS. The headings contained in this Agreement are for
reference purposes only and shall not affect in any way the meaning or
interpretation of this Agreement.

         Section 7.10 SEVERABILITY. If any term or other provision of this
Agreement is invalid, illegal or incapable of being enforced by any rule of law,
or public policy, all other conditions and provisions of this Agreement shall
nevertheless remain in full force and effect so long as the economic or legal
substance of the transactions contemplated hereby is not affected in any manner
adverse to any party. Upon such determination that any term or other provision
is invalid, illegal or incapable of being enforced, the parties hereto shall
negotiate in good faith to modify this Agreement so as to effect the original
intent of the parties as closely as possible in an acceptable manner to the end
that the transactions contemplated hereby are fulfilled to the fullest extent
possible.

         Section 7.11 ENTIRE AGREEMENT. This Agreement constitutes the entire
agreement and supersedes all prior agreements and undertakings (other than the
Confidentiality Agreement
<PAGE>
                                                                 Page 185 of 229

dated as of March 1, 1999 between Oak Investment Partners and the Company), both
written and oral, among the parties, or any of them, with respect to the subject
matter hereof.

         Section 7.12 ASSIGNMENT. This Agreement shall not be assigned by
operation of law or otherwise, except that each Purchaser may assign this
Agreement to any direct or indirect wholly-owned subsidiaries of its ultimate
parent and to any limited partners of any Purchaser and to any affiliate or
sidecar fund of any such Purchaser; PROVIDED, HOWEVER, that the Purchasers'
rights pursuant to Section 4.10 may be assigned only to direct or indirect
wholly- owned subsidiaries of any Purchaser's ultimate parent, unless the
Company's prior written consent is obtained, such consent not to be unreasonably
withheld. Such assignment shall not be valid unless as a condition to such
assignment, the person to whom this Agreement is assigned (i) delivers to the
Company a written instrument by which such person agrees to be bound by the
obligations imposed upon the Purchasers under this Agreement to the same extent
as if such person had been an original Purchaser hereunder and (ii) becomes a
Purchaser hereunder.

         Section 7.13 PARTIES IN INTEREST. This Agreement shall be binding upon
and inure solely to the benefit of each party hereto, and nothing in this
Agreement, express or implied, is intended to or shall confer upon any other
person any right, benefit or remedy of any nature whatsoever under or by reason
of this Agreement, including, without limitation, by way of subrogation.

         Section 7.14 FAILURE OR INDULGENCE NOT WAIVER; REMEDIES CUMULATIVE. No
failure or delay on the part of any party hereto in the exercise of any right
hereunder shall impair such right or be construed to be a waiver of, or
acquiescence in, any breach of any representation, warranty or agreement herein,
nor shall any single or partial exercise of any such right preclude any other or
further exercise thereof or of any other right. All rights and remedies existing
under this Agreement are cumulative to, and not exclusive of, any rights or
remedies otherwise available.

         Section 7.15 GOVERNING LAW. This Agreement shall be governed by, and
construed in accordance with, the internal laws of the State of New York
applicable to contracts executed and fully performed within the State of New
York.

         Section 7.16 COUNTERPARTS. This Agreement may be executed in one or
more counterparts, and by the different parties hereto in separate counterparts,
each of which when executed shall be deemed to be an original but all of which
taken together shall constitute one and the same agreement.



                     [This space intentionally left blank.]

<PAGE>
                                                                 Page 186 of 229

         IN WITNESS WHEREOF, the Company and the Purchasers have caused this
Preferred Stock Purchase Agreement to be executed as of the date first above
written by their respective officers thereunto duly authorized.



The Company:                 ADVANCED RADIO TELECOM CORP.


                             By: /s/ HENRY C. HIRSCH
                                 -----------------------------------------------
                                 Name: Henry C. Hirsch
                                 Title:   Chairman and CEO


The Purchasers:              U.S. TELESOURCE, INC.

                             By: /s/ MARC B. WEISBERG
                                 -----------------------------------------------
                                 Name:  Marc B. Weisberg
                                 Title:


                             OAK INVESTMENT PARTNERS VIII, LIMITED PARTNERSHIP

                             By:  Oak Associates VIII, LLC, General Partner

                             /s/ BANDEL L. CARANO
                             ---------------------------------------------------
                             By: Bandel L. Carano, Managing Member


                             OAK VIII AFFILIATE FUND, LIMITED PARTNERSHIP

                             By: Oak VIII Affiliates, LLC, General Partner
                             ---------------------------------------------------
                             /s/ BANDEL L. CARANO
                             By: Bandel L. Carano, Managing Member

<PAGE>
                                                                 Page 187 of 229


                                       MERITECH CAPITAL AFFILIATES L.P.

                                       By:  MeriTech Capital Associates, L.L.C.
                                            its General Partner

                                       By:  MeriTech Management L.L.C.
                                            a managing member

                                       By: /s/ PAUL MADERA
                                          --------------------------------------
                                               Paul Madera, a managing member


                                       MERITECH CAPITAL PARTNERS L.P.

                                       By:  MeriTech Capital Associates L.L.C.
                                            its General Partner

                                       By:  MeriTech Management L.L.C.
                                            a managing member

                                       By: /s/ PAUL MADERA
                                          --------------------------------------
                                               Paul Madera, a managing member


<PAGE>
                                                                 Page 188 of 229

                                  ACCEL VI L.P.
                                  BY:  ACCEL VI ASSOCIATES L.L.C.
                                  ITS GENERAL PARTNER

                                  By: /s/ G. CARTER SEDNAOUI
                                     ------------------------------
                                     Managing Member


                                  ACCEL INTERNET FUND II L.P.
                                  BY:  ACCEL INTERNET FUND II ASSOCIATES L.L.C.
                                  ITS GENERAL PARTNER

                                  By: /s/ G. CARTER SEDNAOUI
                                     ------------------------------
                                     Managing Member


                                  ACCEL KEIRETSU VI L.P.
                                  By:  ACCEL KEIRETSU VI ASSOCIATES L.L.C.
                                  ITS GENERAL PARTNER

                                  By:/s/ G. CARTER SEDNAOUI
                                     ------------------------------
                                     Managing Member


                                  ACCEL INVESTORS '98 L.P.

                                  By:/s/ G. CARTER SEDNAOUI
                                     ------------------------------
                                     General Partner

<PAGE>
                                                                 Page 189 of 229



                                    BRENTWOOD ASSOCIATES IX, L.P.
                                    By Brentwood IX Ventures, L.L.C.
                                    Its General Partners

                                    By: /s/    JOHN L. WALECKA
                                       -----------------------------------------
                                       Name:   John L. Walecka
                                       Title:  Managing Member

                                    BRENTWOOD AFFILIATES FUND III, L.P.
                                    By Brentwood IX Ventures, L.L.C.
                                    Its General Partner

                                    By: /s/    JOHN L. WALECKA
                                       -----------------------------------------
                                       Name:   John L. Walecka
                                       Title:  Managing Member


                                          COLUMBIA CAPITAL ARTT INVESTORS,
                                               LLC
                                          By:  Columbia Capital, L.L.C.
                                          Its: Managing Member


                                          By: /s/     JAMES B. FLEMING, JR.
                                              ----------------------------------
                                              Name:   James B. Fleming, Jr.
                                              Title:  Managing Director


                                          COLUMBIA CAPITAL ARTT PARTNERS, LLC
                                          By:  Columbia Capital, L.L.C.
                                          Its: Managing Member


                                          By: /s/     JAMES B. FLEMING, JR.
                                              ----------------------------------
                                              Name:   James B. Fleming, Jr.
                                              Title:  Managing Director


<PAGE>
                                                                 Page 190 of 229

                              WORLDVIEW TECHNOLOGY PARTNERS II, L.P.
                              By:   Worldview Capital II, L.P., General Partner
                              By:   Worldview Equity I, L.L.C., General Partner

                              By: /s/ JAMES WEI
                                  ----------------------------------------------
                                  Name: James Wei
                                  Title: Member

                              WORLDVIEW TECHNOLOGY INTERNATIONAL II, L.P.
                              By:  Worldview Capital II, L.P., General Partner
                              By:  Worldview Equity I, L.L.C., General Partner

                              By: /s/ JAMES WEI
                                  ----------------------------------------------
                                  Name: James Wei
                                  Title: Member

                              WORLDVIEW STRATEGIC PARTNERS II, L.P.
                              By:  Worldview Capital II, L.P., General Partner
                              By:  Worldview Equity I, L.L.C., General Partner

                              By: /s/ JAMES WEI
                                  ----------------------------------------------
                                  Name: James Wei
                                  Title:  Member



<PAGE>
                                                                 Page 191 of 229


                             GLOBAL PRIVATE EQUITY II - EUROPE
                             LIMITED PARTNERSHIP


                             GLOBAL PRIVATE EQUITY II - PGGM
                             LIMITED PARTNERSHIP


                             DIGITAL MEDIA AND COMMUNICATIONS II
                             LIMITED PARTNERSHIP


                             OAKSTONE VENTURES LIMITED PARTNERSHIP


                             ADVENT CROWN FUND II C.V.


                             ADWEST LIMITED PARTNERSHIP

                             By:   Advent International Limited Partnership,
                                   General Partner
                             By:   Advent International Corporation,
                                   General Partner
                             By:   Andrew Fillat, Senior Vice President*


                             ADVENT GLOBAL GECC LIMITED PARTNERSHIP

                             By:   Advent Global Management Limited Partnership,
                                   General Partner
                             By:   Advent International Limited Partnership,
                                   General Partner
                             By:   Advent International Corporation,
                                   General Partner
                             By:   Andrew Fillat, Senior Vice President*


                             ADVENT PARTNERS LIMITED PARTNERSHIP
                             By:   Advent International Corporation,
                                   General Partner
                             By:   Andrew Fillat, Senior Vice President*

                             *For all of the above:

                             /s/ ANDREW FILLAT
                             -------------------------------------------------
                             Andrew Fillat, Senior Vice President


<PAGE>
                                                                 Page 192 of 229


                                  BESSEMER VENTURE PARTNERS IV L.P.
                                  By:   Deer IV & Co. LLC, General Partner

                                  By: /s/ ROBERT H. BUESCHER
                                     -------------------------------------------
                                     Name: Robert H. Buescher
                                     Title: Manager


                                  BESSEC VENTURES IV L.P.
                                  By:   Deer IV & Co. LLC, General Partner

                                  By: /s/ ROBERT H. BUESCHER
                                     -------------------------------------------
                                     Name: Robert H. Buescher
                                     Title: Manager

<PAGE>
                                                                 Page 193 of 229


                            COVE VENTURES, LLC
                            By: Cove Road Associates, LLC, Managing Member

                            By: /s/ ROBERT GOODMAN
                                ------------------------------------------
                                Name:  Robert Goodman
                                Title:  Managing Member

<PAGE>
                                                                 Page 194 of 229

                         ADAMS CAPITAL MANAGEMENT, L.P.
                         By:   ACM Capital Partners II, L.P., General Partner
                         By:   Joel P. Adams, General Partner


                         By: /s/ JOEL P. ADAMS
                             ------------------------------------------------
                             Name:  Joel P. Adams
                             Title:  General Partner


                                                                 Page 194 of 229
                                    EXHIBIT D


                             STOCKHOLDERS AGREEMENT

                                  by and among

               OAK INVESTMENT PARTNERS VIII, LIMITED PARTNERSHIP,

                  OAK VIII AFFILIATE FUND, LIMITED PARTNERSHIP,

                           MERITECH CAPITAL PARTNERS,

                                 ACCEL PARTNERS,

                         BRENTWOOD ASSOCIATES IX, L.P.,

                       BRENTWOOD AFFILIATES FUND III, L.P.

                     WORLDVIEW TECHNOLOGY PARTNERS II, L.P.,

                  WORLDVIEW TECHNOLOGY INTERNATIONAL II, L.P.,

                     WORLDVIEW STRATEGIC PARTNERS II, L.P.,

                       BESSEMER VENTURE PARTNERS IV L.P.,

                            BESSEC VENTURES IV L.P.,

                               COVE VENTURES, LLC,

                         ADAMS CAPITAL MANAGEMENT, L.P.,

                                COLUMBIA CAPITAL,

             GLOBAL PRIVATE EQUITY II - EUROPE LIMITED PARTNERSHIP,

              GLOBAL PRIVATE EQUITY II - PGGM LIMITED PARTNERSHIP,

            DIGITAL MEDIA AND COMMUNICATIONS II LIMITED PARTNERSHIP,

                     OAKSTONE VENTURES LIMITED PARTNERSHIP,

                           ADVENT CROWN FUND II C.V.,

                           ADWEST LIMITED PARTNERSHIP,

                     ADVENT GLOBAL GECC LIMITED PARTNERSHIP,

                       ADVENT PARTNERS LIMITED PARTNERSHIP

                                       and

                              U.S. TELESOURCE, INC.

                                   dated as of


                                  June 1, 1999

<PAGE>
                                                                 Page 195 of 229

                             STOCKHOLDERS AGREEMENT


         THIS STOCKHOLDERS AGREEMENT (this "Agreement") dated as of June 1, 1999
is made by and among OAK INVESTMENT PARTNERS VIII, LIMITED PARTNERSHIP ("OIP"),
OAK VIII AFFILIATE FUND, LIMITED PARTNERSHIP ("OAF;" OIP and OAF together being
hereinafter referred to as "Oak"), MERITECH CAPITAL PARTNERS ("MeriTech"), ACCEL
PARTNERS, BRENTWOOD ASSOCIATES IX, L.P. ("Brentwood IX"), BRENTWOOD AFFILIATES
FUND III, L.P. ("Brentwood III"; Brentwood IX and Brentwood III collectively
being hereinafter referred to as "Brentwood"), WORLDVIEW TECHNOLOGY PARTNERS II,
L.P. ("WTP"), WORLDVIEW TECHNOLOGY INTERNATIONAL II, L.P. ("WTI"), WORLDVIEW
STRATEGIC PARTNERS II, L.P. ("WSP;" WTP, WTI and WSP collectively being
hereinafter referred to as "Worldview"), BESSEMER VENTURE PARTNERS IV L.P.,
BESSEC VENTURES IV L.P., COVE VENTURES, LLC, ADAMS CAPITAL MANAGEMENT, L.P.,
COLUMBIA CAPITAL ("Columbia"), GLOBAL PRIVATE EQUITY II - EUROPE LIMITED
PARTNERSHIP ("GPEII"), GLOBAL PRIVATE EQUITY II - PGGM LIMITED PARTNERSHIP
("GPEIIPGGM"), DIGITAL MEDIA AND COMMUNICATIONS II LIMITED PARTNERSHIP
("Digital"), OAKSTONE VENTURES LIMITED PARTNERSHIP ("Oakstone"), ADVENT CROWN
FUND II C.V. ("Advent"), ADWEST LIMITED PARTNERSHIP ("Adwest"), ADVENT GLOBAL
GECC LIMITED PARTNERSHIP ("Advent Global"), ADVENT PARTNERS LIMITED PARTNERSHIP
("Advent Partners;" Columbia, GPEII, GPEIIPGGM, Digital, Oakstone, Advent,
Adwest, Advent Global and Advent Partners collectively being hereinafter
referred to as the "Columbia/Advent Stockholders") and U.S. TELESOURCE, INC.
("USTI") (each of which individually is hereinafter referred to as a
"Stockholder" and all of which collectively are hereinafter referred to as the
"Stockholders").

                                    RECITALS

         WHEREAS, the Stockholders and Advanced Radio Telecom Corp., a Delaware
corporation (the "Company"), are party to that certain Preferred Stock Purchase
Agreement of even date herewith (the "Stock Purchase Agreement") pursuant to
which the Company has agreed to sell, and the Stockholders have agreed to
purchase, an aggregate of 2,635,908 shares of Series A Preferred Stock and
501,592 shares of Series B Preferred Stock upon the terms and subject to the
conditions set forth therein (such Series A Preferred Stock and Series B
Preferred Stock together being hereinafter referred to as the "Preferred
Stock"); and

         WHEREAS, the Stockholders desire to set forth certain understandings
with respect to their ownership of certain securities of the Company, such
securities being, to the extent owned by the Columbia/Advent Purchasers, all
shares of Preferred Stock and any and all shares of Common Stock or other equity
securities of the Company into or for which such shares of Preferred Stock may
be converted or exchanged (such shares of Preferred Stock and Common Stock being
hereinafter referred to as the "Columbia/Advent Equity Securities") and, to the
extent owned by any of the other Stockholders, all equity securities of the
Company including, but not limited to, shares of Preferred Stock and any and all
shares of Common Stock or other equity securities of the Company into or for
which the Preferred Stock may be converted or exchanged (all such securities of
the Company, together being hereinafter referred to as "Other

<PAGE>
                                                                 Page 196 of 229

Stockholder Equity Securities", and together with the Columbia/Advent Equity
Securities, the "Equity Securities").

                                    AGREEMENT

         NOW, THEREFORE, in consideration of the premises and the covenants and
agreements contained herein and for good and valuable consideration, the receipt
and sufficiency of which are hereby acknowledged, and intending to be legally
bound, the parties hereto do hereby agree as follows:

                                    ARTICLE 1

                               CERTAIN DEFINITIONS

         As used in this Agreement, the following terms shall have the following
respective meanings (capitalized terms used but not defined herein shall have
the meanings assigned to them in the Stock Purchase Agreement):

         Section 1.1 "Affiliate" shall have the meaning ascribed thereto in Rule
12b-2 promulgated under the Exchange Act as in effect on the date hereof.

         Section 1.2 "Business Plan" means the business plan for the Company
referred to in Section 4.13 of the Stock Purchase Agreement.

         Section 1.3 "Exchange Act" shall mean the Securities Exchange Act of
1934, as amended.

         Section 1.4 "person" shall mean any individual, corporation,
partnership, limited liability company, joint venture, trust, unincorporated
organization, other form of business or legal entity or governmental entity.

                                    ARTICLE 2

               DESIGNATION OF PURCHASER NOMINEES; VOTING AGREEMENT

         Section 2.1 DESIGNATION OF PURCHASER NOMINEES; QUALIFICATIONS; VOTING
AGREEMENT.

         (a) USTI shall designate the initial Purchaser Nominee whose term as a
director of the Company will expire in 2000, and Oak shall designate the initial
Purchaser Nominee whose term as a director of the Company will expire in 2001,
each by written notice to the Company and to the other Stockholders delivered
not later than three business days prior to the Closing Date and, thereafter (so
long as they are entitled to do so under the Stock Purchase Agreement), they
shall each designate any successor to such initial Purchaser Nominee by written
notice to the Company and to the other Stockholders delivered not later than
three business days prior to the date on which shareholder proposals are due as
set forth in the Company's proxy statement for the preceding year. In the event
that any Purchaser Nominee

<PAGE>
                                                                 Page 197 of 229

shall for any reason cease to serve as a director of the Company prior to the
election of his successor, the Stockholder that designated such Purchaser
Nominee shall designate a replacement Purchaser Nominee by written notice to the
Company and to the other Stockholders delivered not later than 20 business days
after the date on which such person shall have ceased to be a director of the
Company.

         (b) Neither USTI nor Oak shall designate any person as a Purchaser
Nominee if (i) such person is not reasonably experienced in business or
financial matters, (ii) such person has been convicted of, or has pled nolo
contendere to, a felony, (iii) the election of such person to the Board would
violate any law, or (iv) any event required to be disclosed pursuant to Item
401(f) of Regulation S-K of the Exchange Act has occurred with respect to such
person.

         (c)  (i) At each annual or special meeting of stockholders of the
Company or in any action by written consent of stockholders of the Company, each
of the Stockholders shall vote any and all Equity Securities of the Company held
by such Stockholder for the election or reelection, as the case may be, of the
Purchaser Nominees to the Board.

              (ii) At each annual or special meeting of stockholders of the
Company or in any action by written consent of stockholders of the Company, for
so long as the transfer restrictions under Section 3.01 of the Standstill
Agreement shall not have been terminated (as opposed merely to their having been
suspended) thereunder and there shall not have occurred both an Oak Transfer
Event and a USTI Transfer Event (each as defined below), each of the
Stockholders other than the Columbia/Advent Stockholders shall vote any and all
Equity Securities of the Company held by such Stockholder with respect to all
other matters that may be submitted to or otherwise come before the stockholders
of the Company for their vote (x) until such time as either (1) Oak, MeriTech
and/or Worldview, individually or in the aggregate, shall have distributed to
their respective limited partners or otherwise transferred to any person other
than any of their respective Affiliates Equity Securities representing in the
aggregate 50% or more of the amount (subject to adjustment from time to time to
reflect intervening subdivisions or combinations of the stock, stock splits,
stock dividends or similar matters) of Equity Securities acquired by USTI on the
Closing Date (the consummation of any transfer that causes such threshold to be
met or exceeded being herein referred to as an "Oak Transfer Event"), or (2)
USTI shall have transferred to any person other than any of its Affiliates
Equity Securities representing in the aggregate 50% or more of the amount
(subject to adjustment from time to time to reflect intervening subdivisions or
combinations of the stock, stock splits, stock dividends or similar matters) of
Equity Securities acquired, in the aggregate, by Oak, MeriTech and Worldview on
the Closing Date (the consummation of any transfer that causes such threshold to
be met or exceeded being herein referred to as a "USTI Transfer Event"), then as
USTI and Oak shall jointly direct (PROVIDED, HOWEVER, that in the event that
USTI and Oak fail to reach an agreement as to such direction with respect to any
matter and/or fail to communicate such direction to the other Stockholders in
sufficient time for the other Stockholders to vote accordingly, then the other
Stockholders shall be free to vote on such matter as they may determine in their
respective sole discretion), (y) from and after the occurrence of an Oak
Transfer Event (but prior to the occurrence of a USTI Transfer Event), then as
USTI shall direct and (z) from and after the occurrence of a USTI Transfer Event
(but prior to the occurrence of an Oak Transfer Event), then as Oak shall
direct. The voting agreement set forth in Section


<PAGE>
                                                                 Page 198 of 229

2.1(c)(ii) may be terminated (i) prior to the occurrence of either an Oak
Transfer Event or a USTI Transfer Event, by mutual written agreement of Oak and
USTI and written notice to the other Stockholders, (ii) from and after the
occurrence of an Oak Transfer Event (but prior to the occurrence of a USTI
Transfer Event), by USTI in its sole discretion by written notice to Oak and the
other Stockholders and (iii) from and after the occurrence of a USTI Transfer
Event (but prior to the occurrence of an Oak Transfer Event), by Oak in its sole
discretion by written notice to USTI and the other Stockholders. Each
Stockholder shall be present, in person or represented by proxy, and shall vote,
at all stockholder meetings of the Company.

         (d) No Stockholder or any person in control (as such term is defined in
the definition of Affiliate) of a Stockholder shall form, join or in any way
participate in concert with any other persons pursuant to any agreement,
understanding or other arrangement, whether written or oral, with respect to
Equity Securities, or deposit any Equity Securities in any voting trust or
subject any Equity Securities to any voting agreement or other arrangement with
similar effect, except, in each instance, for such as are or may be created by
or pursuant to this Agreement.

         (e) The Stockholders acknowledge and agree that the provisions of this
Section 2.1 shall constitute a voting agreement under and for purposes of
Section 218 of the Delaware General Corporation Law. For so long as this
Agreement is in effect, if any Stockholder fails or refuses to vote any or all
of the Equity Securities held by such Stockholder as required by Section 2.1(c),
then without any further action by such Stockholder, each other Stockholder
willing so to vote such voting securities shall have an irrevocable proxy so to
vote those voting securities in accordance with this Agreement, and each
Stockholder hereby grants to the other Stockholders such irrevocable proxy.

         Section 2.2 INSTRUCTIONS TO PURCHASER NOMINEES AND OTHER REPRESENTATIVE
DIRECTORS; BUSINESS PLAN. Each of USTI and Oak shall cause their respective
Purchaser Nominee, subject to the exercise of his or her fiduciary duties, to
vote in accordance with instructions received from each of USTI and Oak, which
instructions shall include direction to vote to approve all actions on the part
of the Company that are required for the implementation of or are otherwise
consistent with the terms of the Business Plan.

                                    ARTICLE 3

                                    TRANSFERS

         Section 3.1 RESTRICTIONS ON TRANSFER.

         (a) The Stockholders acknowledge that the Equity Securities are subject
to certain other restrictions on transfer as set forth in the Stock Purchase
Agreement and the Standstill Agreement, and that the restrictions on transfer
imposed under this Section 3.1 shall be in addition to such other restrictions
on transfer.

         (b) During the period beginning on the date hereof and ending upon the
automatic conversion of the Series A Preferred Stock into Common Stock pursuant
to Section 5.9 of the Certificate of Designation, no Stockholder shall transfer
or contract to transfer any

<PAGE>
                                                                 Page 199 of 229

share of Equity Securities ("Shares") now owned or hereafter acquired by such
Stockholder except for: (i) transfers by a Stockholder to one or more of its
Affiliates (provided that the transferring Stockholder shall require the
Affiliate transferee to agree to be bound by, and to execute and deliver to each
of the other Stockholders a copy of, this Agreement, and that the transferring
Stockholder shall be and remain liable for the compliance with the terms and
conditions of this Agreement by the Affiliate transferee); (ii) transfers
registered pursuant to and in compliance with the terms of the Registration
Rights Agreement; (iii) transfers by way of distribution to the limited partners
of any Stockholder (and transfers by any "affiliate" or "sidecar" fund of any
such distributing Stockholder of that percentage of the total number of Shares
held by such "affiliate" or "sidecar" fund on the Closing Date representing the
same percentage of the total number of Shares held by the distributing
Stockholder on the Closing Date that is so distributed to the Stockholder's
limited partners); PROVIDED, HOWEVER, that no transfer (whether by way of
distribution or otherwise) pursuant to the exceptions provided for in this
Section 3.1(b)(iii) shall be made prior to the day after the day on which the
directors to be elected at the Company's 2000 annual meeting of stockholders are
in fact elected; and (iv) transfers by USTI representing transfers of that same
percentage of the total number of Shares held by USTI on the Closing Date as the
percentage of the total number of Shares held by any other Stockholder on the
Closing Date that has been distributed by such other Stockholder to such other
Stockholder's limited partners pursuant to the exception provided for in Section
3.1(b)(iii).

         (c) Except as otherwise provided by law, if any Stockholder shall
transfer any Shares in contravention of the provisions of Section 3.1(b), the
rights of the transferee or other beneficiary of such transfer shall be
subordinate and subject to the rights and obligations of the Stockholders under
and pursuant to this Agreement. The Stockholders acknowledge and agree that the
restrictions on transfer of Shares set forth in this Article III are reasonable
and necessary to accomplish the purposes of this Agreement, and bear some
reasonably necessary relation to the best interests of the Company.

                                    ARTICLE 4

              CERTAIN REPRESENTATIONS AND WARRANTIES AND COVENANTS

         Section 4.1 LIQUIDATION OR DISTRIBUTION DATES. Schedule 4.1 hereto sets
forth the earliest date on which, under or pursuant to each of their governing
documents or agreements, each of the Stockholders will or may be required to
liquidate or otherwise to distribute the Equity Securities held by each of them,
respectively.

         Section 4.2 MERITECH. The parties acknowledge that, notwithstanding the
preamble hereto, MeriTech has not yet been organized and therefore has not
executed and delivered and is not yet a party to this Agreement. Oak, Worldview,
Accel and Brentwood shall take any and all actions that may be or become
necessary to ensure that promptly after MeriTech is organized and has executed
and delivered the Stock Purchase Agreement, MeriTech shall execute and deliver
and become a party to this Agreement, and Oak, Worldview, Accel and Brentwood
shall ensure the due and timely performance of and compliance with, and, if and
to the extent any of them is not so performed, shall be jointly and severally
responsible to the Stockholders for the performance of, all agreements and
obligations of MeriTech under and

<PAGE>
                                                                 Page 200 of 229

pursuant to this Agreement and the Stock Purchase Agreement. If at any time
MeriTech shall cease to be a party to the Stock Purchase Agreement, at such time
MeriTech also shall cease to be a party to this Agreement.

         Section 4.3 NO INCONSISTENT AGREEMENTS. None of the Stockholders is
party to, and none of them shall enter into, any other agreement with respect to
the voting or transfer or any other indicia of ownership of any Equity
Securities, nor is any of them party to, nor shall any of them enter into, any
other agreement that contains any term or provision that conflicts with or is
inconsistent with the terms and provisions of this Agreement.

         Section 4.4 RELEASE AND DISCHARGE OF USTI AND OAK. Each Stockholder
hereby irrevocably releases and forever discharges each of the USTI and Oak from
any liability or responsibility for any acts performed or omitted to be
performed in directing the vote as contemplated by Section 2.1(c)(ii); PROVIDED,
HOWEVER, that each of USTI and Oak may nevertheless be liable to the other
Stockholders for any act performed or omitted to be performed to the extent
attributable to its gross negligence or willful misconduct.

                                    ARTICLE 5

                                  MISCELLANEOUS

         Section 5.1 COUNTERPARTS. This Agreement may be executed in any number
of counterparts and by different parties in separate counterparts, all of which
shall constitute one and the same agreement, and shall become effective when one
or more counterparts have been signed by each of the parties and delivered to
the other parties.

         Section 5.2 GOVERNING LAW. THIS AGREEMENT SHALL BE GOVERNED BY AND
CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK WITHOUT REFERENCE
TO THE CHOICE OF LAW PRINCIPLES THEREOF.

         Section 5.3 ENTIRE AGREEMENT. This Agreement contains the entire
agreement among the Stockholders with respect to the subject matter hereof. This
Agreement is not intended to confer upon any person not a party hereto (or their
successors and assigns) any rights or remedies hereunder.

         Section 5.4 EXPENSES. Except as otherwise provided in the Stock
Purchase Agreement, all legal and other costs and expenses incurred in
connection with this Agreement and the transactions contemplated hereby shall be
paid by the party incurring such costs and expenses.

         Section 5.5 NOTICES. All notices, requests, consents and other
communications hereunder shall be in writing and shall be deemed to have been
made (i) when delivered personally or by telecopier, (ii) when mailed first
class registered or certified mail, postage prepaid, or (iii) on the day
following deposit with a reputable overnight courier, charges prepaid, to each
respective party as specified in Section 7.3 of the Stock Purchase Agreement.
<PAGE>
                                                                 Page 201 of 229

         Section 5.6 SUCCESSORS AND ASSIGNS. This Agreement shall be binding
upon and inure to the benefit of the parties hereto and nothing in this
Agreement, express or implied, is intended to confer upon any other person any
rights or remedies of any nature whatsoever under or by reason of this
Agreement. Neither this Agreement nor any rights or obligations under it are
assignable by any party hereto, except pursuant to a transfer of Shares
permitted under Section 3.1(b)(i).

         Section 5.7 HEADINGS. The headings in this Agreement are for
convenience only and shall not limit or otherwise affect the meaning hereof.

         Section 5.8 AMENDMENTS AND WAIVERS. This Agreement may be amended only
by agreement in writing of all parties. No waiver of any provision nor consent
to any exception to the terms of this Agreement shall be effective unless in
writing and signed by the party to be bound and then only to the specific
purpose, extent and instance so provided.

         Section 5.9 INTERPRETATION. For the purposes hereof, (i) words in the
singular shall be held to include the plural and vice versa and words of one
gender shall be held to include the other gender as the context requires, (ii)
the terms "hereof", "herein", and "herewith" and words of similar import shall,
unless otherwise stated, be construed to refer to this Agreement as a whole and
not to any particular provision of this Agreement, and Article, Section and
paragraph references are to the Articles, Sections and paragraphs, of this
Agreement unless otherwise specified, (iii) the word "including" and words of
similar import when used in this Agreement shall mean "including, without
limitation," unless the context otherwise requires or unless otherwise
specified, (iv) the word "or" shall not be exclusive, and (v) provisions shall
apply, when appropriate, to successive events and transactions. This Agreement
shall be construed without regard to any presumption or rule requiring
construction or interpretation against the party drafting or causing any
instrument to be drafted.

         Section 5.10 SEVERABILITY. In the event that any one or more of the
provisions contained herein, or the application thereof in any circumstance, is
held invalid, illegal or unenforceable, the validity, legality and
enforceability of any such provision in every other respect and of the remaining
provisions contained herein shall not be affected or impaired thereby.

         Section 5.11 FURTHER ASSURANCES. Each Stockholder agrees that, from
time to time, each of them will, and will cause their respective Affiliates to,
execute and deliver such further instruments and take such other action as may
be necessary to carry out the purposes and intents hereof.

         Section 5.12 SPECIFIC PERFORMANCE. Each of the parties hereto
acknowledges that, in view of the uniqueness of the arrangements contemplated by
this Agreement, each party would not have an adequate remedy at law for money
damages in the event that this Agreement has not been performed in accordance
with its terms, and therefore agree that the other parties hereto shall be
entitled to specific enforcement of the terms hereof in addition to any other
remedy to which the parties hereto may be entitled, at law or in equity.
<PAGE>
                                                                 Page 202 of 229

         Section 5.13 ATTORNEY'S FEES. In the event of any action, complaint,
petition, or other proceeding ("Action") by any party arising under or out of,
in connection with or in respect of, this Agreement, the prevailing party shall
be entitled to reasonable attorney's fees, costs and expenses incurred in such
Action. Attorney's fees incurred in enforcing any judgment in respect of this
Agreement are recoverable as a separate item. The parties intend that the
preceding sentences be severable from the other provisions of this Agreement,
survive any judgment and, to the maximum extent permitted by law, not be deemed
merged into such judgment.

         Section 5.14 EFFECTIVENESS; AUTOMATIC TERMINATION. The covenants set
forth in Articles II and III of this Agreement shall become effective only on
and as of the Closing Date. All other provisions of this Agreement shall become
effective on and as of the date hereof. This Agreement shall automatically
terminate and be of no further force and effect if and when the Stock Purchase
Agreement shall be terminated prior to the Closing pursuant to Section 6.1
thereof.

<PAGE>
                                                                 Page 203 of 229

         IN WITNESS WHEREOF, each Stockholder has caused this Stockholders
Agreement to be executed by its duly authorized representative as of the date
first above written.


                                   OAK INVESTMENT PARTNERS VIII,
                                   LIMITED PARTNERSHIP

                                   By: Oak Associates VIII, LLC, General Partner

                                   /s/ BANDEL L. CARANO
                                   ---------------------------------------------
                                   Name:  Bandel L. Carano, Managing Member



                                   OAK VIII AFFILIATE FUND, LIMITED
                                   PARTNERSHIP

                                   By: Oak VIII Affiliates, LLC, General Partner

                                   /s/ BANDEL L. CARANO
                                   ---------------------------------------------
                                   Name:  Bandel L. Carano, Managing Member

<PAGE>
                                                                 Page 204 of 229


                                                   [Stockholders Agreement]

                                   MERITECH CAPITAL AFFILIATES L.P.

                                   By:  MeriTech Capital Associates, L.L.C.
                                         its General Partner

                                   By:  MeriTech Management L.L.C.
                                         a managing member

                                   By: _________________________________________
                                       Paul Madera, a managing member


                                   MERITECH CAPITAL PARTNERS L.P.

                                   By:  MeriTech Capital Associates L.L.C.
                                         its General Partner

                                   By:  MeriTech Management L.L.C.
                                         a managing member

                                   By: _________________________________________
                                       Paul Madera, a managing member


<PAGE>
                                                                 Page 205 of 229


                                                [Stockholders Agreement]

                             ACCEL VI L.P.
                             BY:  ACCEL VI ASSOCIATES L.L.C.
                             ITS GENERAL PARTNER

                             By: /s/ G. CARTER SEDNAOUI
                                ------------------------------------------------
                                Managing Member


                             ACCEL INTERNET FUND II L.P.
                             BY:  ACCEL INTERNET FUND II ASSOCIATES L.L.C.
                             ITS GENERAL PARTNER

                             By: /s/ G. CARTER SEDNAOUI
                                ------------------------------------------------
                                Managing Member


                             ACCEL KEIRETSU VI L.P.
                             By:  ACCEL KEIRETSU VI ASSOCIATES L.L.C.
                             ITS GENERAL PARTNER

                             By: /s/ G. CARTER SEDNAOUI
                                ------------------------------------------------
                                Managing Member


                             ACCEL INVESTORS '98 L.P.

                             By: /s/ G. CARTER SEDNAOUI
                                ------------------------------------------------
                                General Partner


<PAGE>
                                                                 Page 206 of 229


                                                   [Stockholders Agreement]

                                 BRENTWOOD ASSOCIATES IX, L.P.

                                 By:  Brentwood IX Ventures, L.L.C.
                                 Its General Partners

                                 By: /s/ JOHN L. WALECKA
                                    --------------------------------------------
                                    Name:  John L. Walecka
                                    Title:  Managing Member


                                 BRENTWOOD AFFILIATES FUND III, L.P.

                                 By:  Brentwood IX Ventures, L.L.C.
                                 Its General Partner

                                 By: /s/ JOHN L. WALECKA
                                    --------------------------------------------
                                    Name:  John L. Walecka
                                    Title:  Managing Member

<PAGE>
                                                                 Page 207 of 229


                                             [Stockholders Agreement]

                                 COLUMBIA CAPITAL

                                 By: /s/ JAMES B. FLEMING, JR.
                                    --------------------------------------------
                                    Name: James B. Fleming, Jr.
                                    Title: Managing Director

<PAGE>
                                                                 Page 208 of 229


                                            [Stockholders Agreement]

                              WORLDVIEW TECHNOLOGY
                              PARTNERS II, L.P.

                              By:   Worldview Capital II, L.P., General Partner
                              By:   Worldview Equity I, L.L.C., General Partner

                              By:  /s/ JAMES WEI
                                   --------------------------------------------
                                   Name:  James Wei
                                   Title:  Member


                              WORLDVIEW TECHNOLOGY INTERNATIONAL II, L.P.

                              By:   Worldview Capital II, L.P., General Partner
                              By:   Worldview Equity I, L.L.C., General Partner

                              By:  /s/ JAMES WEI
                                   --------------------------------------------
                                   Name:  James Wei
                                   Title:  Member


                              WORLDVIEW STRATEGIC
                              PARTNERS II, L.P.

                              By:   Worldview Capital II, L.P., General Partner
                              By:   Worldview Equity I, L.L.C., General Partner

                              By:  /s/ JAMES WEI
                                   --------------------------------------------
                                   Name:  James Wei
                                   Title:  Member

<PAGE>
                                                                 Page 209 of 229


                                                 [Stockholders Agreement]

                           GLOBAL PRIVATE EQUITY II - EUROPE
                           LIMITED PARTNERSHIP


                           GLOBAL PRIVATE EQUITY II - PGGM
                           LIMITED PARTNERSHIP


                           DIGITAL MEDIA AND COMMUNICATIONS
                           II LIMITED PARTNERSHIP


                           OAKSTONE VENTURES LIMITED
                           PARTNERSHIP


                           ADVENT CROWN FUND II C.V.


                           ADVENT LIMITED PARTNERSHIP

                           By:   Advent International Limited Partnership,
                                 General Partner
                           By:   Advent International Corporation,
                                 General Partner
                           By:   Andrew Fillat, Senior Vice President*

                           ADVENT GLOBAL GECC LIMITED
                           PARTNERSHIP

                           By:   Advent Global Management Limited Partnership,
                                 General Partner
                           By:   Advent International Limited Partnership,
                                 General Partner
                           By:   Advent International Corporation,
                                 General Partner
                           By:   Andrew Fillat, Senior Vice President*

                           ADVENT PARTNERS LIMITED
                           PARTNERSHIP

                           By:   Advent International Corporation,
                                 General Partner
                           By:   Andrew Fillat, Senior Vice President*

                           *For all of the above:

                           /s/ ANDREW FILLAT
                           ---------------------------------------------------
                           Andrew Fillat, Senior Vice President

<PAGE>
                                                                 Page 210 of 229

                                                    [Stockholders Agreement]


                                     BESSEMER VENTURE PARTNERS IV L.P.

                                     By: Deer IV & Co. LLC, General Partner

                                     By: /s/ ROBERT H. BUESCHER
                                         ---------------------------------------
                                         Name:  Robert H. Buescher
                                         Title:  Manager

                                     BESSEC VENTURES IV L.P.

                                     By: Deer IV & Co. LLC, General Partner

                                     By: /s/ ROBERT H. BUESCHER
                                         ---------------------------------------
                                         Name:  Robert H. Buescher
                                         Title:  Manager

                                     COVE VENTURES, LLC

                                     By: Cove Road Associates, LLC,
                                         Managing Member

                                     By: /s/ ROBERT GOODMAN
                                         ---------------------------------------
                                         Name:  Robert Goodman
                                         Title:  Managing Member

<PAGE>
                                                                 Page 211 of 229


                                                 [Stockholders Agreement]


                            ADAMS CAPITAL MANAGEMENT, L.P.
                            By:  ACM Capital Partners II, L.P., General Partner
                            By:  Joel P. Adams, General Partner

                            By: /s/ JOEL P. ADAMS
                                ------------------------------------------------
                                Name:  Joel P. Adams
                                Title:  General Partner
<PAGE>
                                                                 Page 212 of 229


                                               [Stockholders Agreement]


                              U.S. TELESOURCE, INC.


                              By: /s/ MARC B. WEISBERG
                                  ----------------------------------------------
                                  Name: Marc B. Weisberg
                                  Title: President and Chief Executive Officer


                                                                 Page 213 of 229

                                    EXHIBIT E


                              STANDSTILL AGREEMENT

         This Standstill Agreement (the "Agreement"), dated as of June 1, 1999,
is between Advanced Radio Telecom Corp., a Delaware corporation (the "Company")
and each of the parties listed on Schedule I hereto (the "Purchasers").

         WHEREAS, simultaneously with the execution of this Agreement, the
Purchasers are entering into an agreement to purchase shares of the Company's
Series A and Series B Convertible Preferred Stock (the "Preferred Stock")
pursuant to the Stock Purchase Agreement (the "Purchase Agreement") among the
Company and the Purchasers dated as of the date hereof; and

         WHEREAS, the Company and each of the Purchasers desire to establish in
this Agreement certain conditions of such Purchaser's and such Purchaser's
Affiliates' relationship with Company;

         NOW, THEREFORE, in consideration of the mutual covenants and agreements
contained herein and in the Agreement, the parties hereto agree as follows:

                                    ARTICLE I

                                   DEFINITIONS

         SECTION 1.01      DEFINITIONS.

                  (a) "ACQUISITION PROPOSAL" shall mean a bona fide, written
         proposal, which proposal includes all material terms of a proposed
         transaction, received by the Board of Directors of the Company from any
         Person or Group proposing to enter into a transaction which, if
         effected, would constitute a Change of Control of the Company.

                  (b) "AFFILIATE" shall have the meaning given it in Rule 12b-2
         under the Exchange Act.

                  (c) "ASSOCIATE" shall have the meaning given it in Rule 12b-2
         under the Exchange Act.

                  (d) "BENEFICIAL OWNER" shall have the meaning given it in Rule
         13(d)(3) under the Exchange Act; and "Beneficially Own" and "Beneficial
         Ownership" shall apply to securities held by a Beneficial Owner.

                  (e) "CHANGE OF CONTROL" shall mean (1) the acquisition by a
         Third Party of more than 50% of the Company's then outstanding Voting
         Stock, excluding however, a purchase agreement with an underwriter or
         group of underwriters in a registered public offering to the public;
         (2) the consummation of a merger, acquisition, consolidation or
<PAGE>
                                                                 Page 214 of 229

         reorganization or series of such related transactions involving the
         Company, unless both (x) immediately after such transaction or
         transactions, the stockholders of the Company immediately prior to such
         transaction shall Beneficially Own at least 50% of the outstanding
         Voting Stock of the Company (or, if the Company shall not be the
         surviving company in such merger, consolidation or reorganization, the
         Voting Stock of the surviving corporation issued in such transaction in
         respect of Voting Stock of the Company shall represent at least 50% of
         the Voting Stock of such surviving company), and (y) the Company is not
         subject to an agreement that provides that individuals who are
         directors of the Company immediately prior to such transaction (or
         individuals designated by the Company at or before the closing of such
         transaction) shall constitute less than a majority of the directors of
         the Company (or such surviving company, as the case may be) after the
         closing of such transaction; (3) a change or changes in the membership
         of the Company's Board of Directors which represents a change of a
         majority or more of such membership during any twelve month period
         (unless such change or changes in membership are caused by the actions
         of the then-existing Board of Directors); (4) an Insolvency Proceeding
         (as defined below); or (5) the consummation of a sale of all or
         substantially all of the Company's assets unless immediately after such
         transaction, the stockholders of the Company immediately prior to such
         transaction shall beneficially own at least 50% of the Voting Stock of
         the acquiring company.

                  (f) "EXCHANGE ACT" shall mean the Securities Exchange Act of
         1934, as amended.

                  (g) "GROUP" shall have the meaning provided in Section
         13(d)(3) of the Exchange Act.

                  (h) "INSOLVENCY PROCEEDING" shall mean (1) an assignment for
         the benefit of creditors, (2) the filing by the Company of a petition
         to have the Company adjudged insolvent, bankrupt or seeking a
         reorganization or liquidation under any law relating to bankruptcy,
         insolvency or receivership, (3) an appointment of a receiver or trustee
         for all or substantially all of the assets of the Company unless
         appointed without the Company's consent, in which case if after 60 days
         such appointment has not been vacated or stayed, (4) a public admission
         in writing of the Company's inability to pay its debts as they come
         due, or (5) the adoption of a plan of liquidation or dissolution by the
         Board of Directors of the Company.

                  (i) "PERSON" means an individual, corporation, partnership,
         association, trust, unincorporated organization or other entity.

                  (j) "STOCKHOLDERS AGREEMENT" shall mean the Stockholders
         Agreement in the form attached as Exhibit A, and as amended with the
         agreement of the Company.

                  (k) "THIRD PARTY" shall mean any Person (other than any
         Purchaser and its Affiliates and Associates) or Group (other than any
         Group that includes any Purchaser or its Affiliates or Associates).
<PAGE>
                                                                 Page 215 of 229

                  (l) "TOTAL VOTING POWER" at any date, with respect to any
         Person, shall mean the total combined Voting Power of all the Voting
         Stock of such Person then outstanding and entitled to vote.

                  (m) "TWO-THIRDS IN INTEREST" means, prior to the closing of
         the transactions contemplated by the Purchase Agreement, Purchasers
         (and permitted assignees) who have agreed to purchase more than 66 2/3%
         of the shares of Preferred Stock pursuant to the Purchase Agreement
         and, on and after the closing of the transactions contemplated by the
         Purchase Agreement, Purchasers (and transferees, pursuant to Section
         4.01(a) hereof) holding more than 66 2/3% of the shares of Preferred
         Stock purchased pursuant to the Purchase Agreement then owned by the
         Purchasers.

                  (n) "VOTING POWER" with respect to any Voting Securities of
         any Person on any date shall mean the voting power in the general
         election of directors of the relevant Person to which such Voting
         Securities would be entitled on such date.

                  (o) "VOTING STOCK" of any Person shall mean any securities
         entitled to vote generally in the election of directors of such Person,
         or any direct or indirect rights or options or warrants to acquire any
         such securities or any securities (including, without limitation, the
         Preferred Stock) convertible or exercisable into or exchangeable for
         such securities, whether or not such securities are so convertible,
         exercisable or exchangeable at the time of determination.

                                   ARTICLE II

                                      TERM


         SECTION 2.01 TERM. The term (the "Term") of this Agreement shall
commence on the date hereof and shall continue until the earliest to occur of
the following:

                  (a) the fourth anniversary of the Closing under the Purchase
         Agreement;

                  (b) the termination of the Purchase Agreement prior to the
         Closing in accordance with its terms; and

                  (c) the date, following the Closing, on which the Company has
         no further obligations under Section 4.9 of the Purchase Agreement with
         respect to the election to the Company's Board of Directors of any
         nominee of UST or Oak Investment Partners and no nominee of UST or Oak
         Investment Partners designated and elected to the Company's Board of
         Directors pursuant to the provisions of Section 4.9 of the Purchase
         Agreement is a director of the Company.
<PAGE>
                                                                 Page 216 of 229
                                   ARTICLE III

                              STANDSTILL PROVISIONS

         SECTION 3.01 RESTRICTIONS OF CERTAIN ACTIONS. Each of the Purchasers
hereby severally agrees that during the Term, neither it nor any Affiliate or
Associate of such Purchaser will, singly or as part of a Group, directly or
indirectly:

                  (a) acquire or offer, make a proposal or agree to acquire
         (whether publicly or otherwise), in any manner, any material assets of
         the Company or its subsidiaries or any equity securities of the Company
         or its subsidiaries (or Beneficial Ownership thereof), except (1)
         pursuant to a stock split, stock dividend, recapitalization,
         reclassification or similar transaction not effected pursuant to a
         violation of this Section 3.01, (2) upon the conversion of the
         Preferred Stock into Common Stock in accordance with the Company's
         Certificate of Incorporation, (3) pursuant to the Rights Agreement
         dated as of June 20, 1997 between the Company and BankBoston, N.A. or
         (4) pursuant to the exercise of rights pursuant to Section 4.16 of the
         Purchase Agreement.

                  (b) make or in any way propose or participate in any
         "solicitation" of "proxies" to vote (as such terms are defined in Rule
         14a-1 under the Exchange Act), solicit any consent or communicate with
         or seek to advise or influence any Person, other than the Company, with
         respect to the solicitation or voting of any Voting Securities of the
         Company in opposition to any matter that has been recommended by the
         Board or in favor of any matter that has not been approved by the
         Board, or become a "participant" in any "election contest" (as such
         terms are defined or used in Rule 14a-11 under the Exchange Act) with
         respect to Company except pursuant to the Stockholders Agreement.

                  (c) form, be a member of, join or encourage the formation of,
         any Group with respect to any Voting Securities of the Company or the
         acquisition of any assets of the Company other than any such Group
         resulting from, and solely to the extent set forth in, the Stockholders
         Agreement;

                  (d) deposit any Voting Stock of the Company into a voting
         trust or subject any such Voting Stock to any arrangement or agreement
         with respect to the voting thereof other than the Stockholders
         Agreement;

                  (e) seek election to or seek to place a representative on the
         Board of Directors of the Company (except pursuant to Section 4.10 of
         the Purchase Agreement or Section 4.4 of the Certificate of Designation
         (the "Certificate") relating to the Preferred Stock and except for any
         chief executive officer of the Company) or seek the removal of any
         member of the Board of Directors the Company other than pursuant to the
         Stockholders Agreement or the Certificate;

                  (f) call or seek to have called any meeting of the
         stockholders of Company other than participation as a director of the
         Company in calling, or seeking to have called, meetings of stockholders
         generally;
<PAGE>
                                                                 Page 217 of 229

                  (g) solicit, seek to effect, negotiate with or provide any
         information to any other party with respect to, or make any statement
         or proposal, whether written or oral, to the Board of Directors of
         Company or otherwise make any public announcement or proposal
         whatsoever with respect to a merger or acquisition of the Company the
         sale of all or a substantial portion of the assets of the Company and
         its subsidiaries, liquidation of the Company, recapitalization of the
         Company or similar business transactions with respect to the Company or
         take any action which might require either party to make a public
         announcement with respect to any such matters (the foregoing shall not
         limit the Purchaser from discussing any Third Party Acquisition
         Proposal with, or providing any information with respect thereto to,
         the Company or other Purchasers); or

                  (h) instigate, encourage or assist, or enter into any
         discussions or arrangements with, any Third Party to do any of the
         actions described in Sections 3.01(a) through (h) (the foregoing shall
         not limit the Purchaser from discussing any Third Party Acquisition
         Proposal with the Company or other Purchasers);

                  (i) If any Purchaser or any of its Affiliates or Associates
         owns or acquires any Voting Securities in violation of this Agreement,
         such Voting Securities shall immediately be disposed of to persons who
         are not Affiliates or Associates thereof but only in compliance with
         the provisions of this Section 3.01 and Section 4.01; PROVIDED,
         HOWEVER, that Company may also pursue any other available remedy to
         which it may be entitled as a result of such violation.

Notwithstanding the restrictions contained in this Section 3.01, the Purchasers
shall not be prevented from complying with the requirements of Sections 13(d)
and 16(a) of the Exchange Act and the rules and regulations thereunder, in each
case, as from time to time in effect, or any successor provisions or rules with
respect thereto, or any other applicable law or rule or regulation of any
governmental body. Notwithstanding the restrictions contained in this Section
3.01, if, prior to the Closing (as defined in the Purchase Agreement), the
Company receives an Acquisition Proposal from a Third Party and the Company (i)
publicly announces that it is considering the Acquisition Proposal or that it is
engaged in discussions with respect to a sale or other transaction involving a
Change of Control, (ii) withdraws or modifies its approval of the Stock Purchase
(as defined in the Purchase Agreement) or (iii) notifies the Purchasers of its
intent to terminate the Purchase Agreement pursuant to Section 6.1 (f) of the
Purchase Agreement (each of the foregoing is a "Limited Trigger") then the
Purchasers shall be free to take any action otherwise prohibited by Sections
3.01(a) (but limited to any acquisition from, offer to, proposal to or agreement
with the Company or its subsidiaries), 3.01(b), 3.01(c), 3.01(g) or 3.01(h) in
contemplation of, and to make, an Acquisition Proposal to be made during the
period from the occurrence of the Limited Trigger until the Company notifies the
Purchasers that the Company has rejected such Acquisition Proposal.

         SECTION 3.02 SUSPENSION OF RESTRICTIONS. The limitations provided in
Section 3.01 and Section 4.01 shall immediately be suspended upon the occurrence
of any of the following events.
<PAGE>
                                                                 Page 218 of 229

                  (a) any Third Party commences a tender or exchange offer
         seeking to acquire Beneficial Ownership of 50% or more of the
         outstanding shares of Voting Stock, but only if (i) the Company has not
         within 10 days after commencement of such offer (or such longer period
         as may then be permitted under applicable law for the Company's initial
         recommendation with respect to such offer), publicly recommended that
         such offer not be accepted, or (ii) all of the material conditions to
         such offer relating to the elimination or satisfaction of the material
         defensive provisions established by the Company, including any rights
         plan or similar defensive provision of the Company have been satisfied
         or waived;

                  (b) the Company's receipt of an Acquisition Proposal from any
         Third Party but only if the Company has not, within 15 days after such
         receipt, rejected such Acquisition Proposal;

                  (c)      the occurrence of a Change of Control of the Company;

                  (d) the public announcement by the Company that it is "for
         sale";

                  (e) the execution of a definitive agreement which, if
         consummated, would result in a Change of Control of the Company;

                  (f) the public announcement by or on behalf of any Person or
         Group (other than the Purchaser and its Affiliates) of the commencement
         of a bona fide proxy or consent solicitation subject to Section 14 of
         the Exchange Act (or any successor provision) to elect or remove a
         majority of the directors of the Company which is not, within 10 days
         after the announcement of such proxy or consent solicitation (or such
         longer period as may then be permitted under applicable law for the
         Company's initial recommendation with respect to such contest if such a
         period is specified) publicly opposed by the Company's Board of
         Directors and which would, if successful, result in a change in the
         composition of a majority of the Board of Directors of the Company; or

                  (g) the adoption by the Board of Directors of a plan of
liquidation or dissolution.

         The Company shall provide the Purchaser with prompt written notice of
the occurrence of any of the events set forth in this Section 3.01 or of the
receipt by the Company of an Acquisition Proposal from any Third Party (such
notice to be provided within ten days after receipt thereof, but without
disclosing the terms thereof or the identity of such Third Party). Upon any (i)
withdrawal or lapsing of any such tender or exchange offer referred to in
Section 3.02(a) in which such Third Party does not acquire more than 15% of the
outstanding Voting Stock of the Company, (ii) withdrawal, rejection or
termination of an Acquisition Proposal referred to in Section 3.02(b), (iii) the
public withdrawal of any "for sale" notice referred to in Section 3.02(d), (iv)
the termination of the agreement referred in Section 3.02(e) without
consummation thereof, (v) the withdrawal or termination or failure of the
solicitation referred to in Section 3.02(f) or (vi) the termination of the plan
of liquidation referenced in Section 3.02(g), as the case may be, the
limitations provided in Sections 3.01 and 4.01 (except to the extent then
<PAGE>
                                                                 Page 219 of 229

suspended as a result of any other event specified in Section 3.02) shall again
be applicable for so long as and only to the extent provided therein without any
extension of the term thereof.

                                   ARTICLE IV

                              TRANSFER RESTRICTIONS

         SECTION 4.01 PERMITTED TRANSFERS. During the Term, but only until the
second anniversary of the Closing under the Purchase Agreement, the Purchaser
shall not sell, pledge, hypothecate, assign or otherwise transfer (each a
"Transfer") any Voting Securities of the Company other than the following
Transfers:

                  (a) A Transfer to an Affiliate of such Purchaser, provided
         that such Affiliate becomes a party to, and agrees to be bound by, this
         Agreement;

                  (b) A Transfer by partnerships by way of distribution to a
         limited partner or former limited partner of such Purchaser that is not
         an Affiliate of such Purchaser;

                  (c) A private Transfer (i) to any "person" (within the meaning
         of Section 13(d)(3) of the Exchange Act), that is not an Affiliate or
         Associate of such Purchaser, which to the knowledge of the Purchaser
         after inquiry beneficially owns or, as a result of such sale or
         transfer, will beneficially own less than ten percent (10%) of the
         Total Voting Power of the Company (a "Permitted Transferee"), PROVIDED,
         THAT such person will not be Permitted Transferee and no such transfer
         shall be permitted if such person, has proposed a business combination
         or similar transaction with, or a Change of Control of the Company or
         (ii) to an account managed by an institutional manager described in
         Rule 13f-1 of the Exchange Act with respect to which the transferred
         Voting Securities would constitute "Section 13(f) securities" within
         the meaning of Rule 13f-1(c) of the Exchange Act; and

                  (d) a sale to the public (i) pursuant to Rule 144 of the
         Securities Act or (ii) pursuant to the exercise by the Purchasers of
         their rights under the Registration Rights Agreement.

                                    ARTICLE V

                                  MISCELLANEOUS

         SECTION 5.01 ENFORCEMENT. Each of the Purchasers, on the one hand, and
Company, on the other, acknowledge and agree that irreparable damage would occur
if any of the provisions of this Agreement were not performed in accordance with
their specific terms or were otherwise breached. Accordingly, the parties will
be entitled to an injunction or injunctions to prevent breaches of this
Agreement and to enforce specifically its provisions in any court having
jurisdiction, this being in addition to any other remedy to which they may be
entitled at law or in equity.
<PAGE>
                                                                 Page 220 of 229

         SECTION 5.02 ENTIRE AGREEMENT; WAIVERS. This Agreement, the Purchase
Agreement, the Stockholder Agreement and the Registration Rights Agreement
constitute the entire agreement among the parties hereto pertaining to the
subject matter hereof and thereof and supersede all prior and contemporaneous
agreements, understandings, negotiations and discussions, whether oral or
written, of the parties with respect to such subject matter. No waiver of any
provision of this Agreement shall be deemed or shall constitute a waiver of any
other provision hereof (whether or not similar), shall constitute a continuing
waiver unless otherwise expressly provided nor shall be effective unless in
writing and executed (i) in the case of a waiver by Company, by the Company and
(ii) in the case of a waiver by the Purchasers, by "Two-Thirds in Interest" of
the Purchasers.

         SECTION 5.03 AMENDMENT OR MODIFICATION. The parties hereto may not
amend or modify this Agreement except in such manner as may be agreed upon by a
written instrument executed by the Company and Two-Thirds in Interest of the
Purchasers.

         SECTION 5.04 SUCCESSORS AND ASSIGNS. All the terms and provisions of
this Agreement shall be binding upon and shall inure to the benefit of the
parties hereto and their respective transferees, successors and assigns (each of
which such transferees, successors and assigns shall be deemed to be a party
hereto for all purposes hereof); PROVIDED, HOWEVER, that (i) neither Company nor
any Purchaser may assign or transfer any of its rights or obligations hereunder
without the prior written consent of the Two-Thirds in Interest of the
Purchasers or the Company, respectively and (ii) no transfer or assignment by
any party shall relieve such party of any of its obligations hereunder.

         SECTION 5.05 SEVERABILITY. If any provision of this Agreement is held
by a court of competent jurisdiction to be unenforceable, the remaining
provisions shall remain in full force and effect. It is declared to be the
intention of the parties that they would have executed the remaining provisions
without including any that may be declared unenforceable.

         SECTION 5.06 HEADINGS. Descriptive headings are for convenience only
and will not control or affect the meaning or construction of any provision of
this Agreement.

         SECTION 5.07 COUNTERPARTS. For the convenience of the parties, any
number of counterparts of this Agreement may be executed by the parties, and
each such executed counterpart will be an original instrument.

         SECTION 5.08 NOTICES. Any notices or other communications required or
permitted hereunder shall be sufficiently given if in writing (including
telecopy or similar teletransmission), addressed as follows:
<PAGE>
                                                                 Page 221 of 229

                      If to the Company, to:

                      Advanced Radio Telecom Corp.
                      500 108th Avenue NE, Suite 2600
                      Bellevue, WA  98004
                      Attn: Thomas M. Walker, Esq., General Counsel
                      Telecopier No: (425) 990-1642 or (425) 688-0703
                      Telephone No:  (425) 990-1669

                      with a copy to:

                      Ropes & Gray
                      One International Place
                      Boston, MA  02110
                      Attn: Mary E. Weber, Esq.
                      Telecopier No: (617) 951-7050
                      Telephone No: (617) 951-7391

                  (a) if to the Purchasers, to such address listed on Schedule I
         to the Purchase Agreement, with a copy to:

                      Gunderson Dettmer Stough Villeneuve Franklin
                         & Hachigian, LLP
                      155 Constitution Drive
                      Menlo Park, CA  94025
                      Attn:  Brooks Stough, Esq.
                      Telecopier No:  (650) 321-2800
                      Telephone No:  (650) 463-5370

                      O'Melveny & Myers, LLP
                      1999 Avenue of the Stars
                      Los Angeles, California  90067-6035
                      Attn:  Steven Grossman, Esq.
                      Telecopier No: (310) 246-6779
                      Telephone No:  (310) 553-6700

Unless otherwise specified herein, such notices or other communications shall be
deemed received (a) in the case of any notice or communication sent other than
by mail, on the date actually delivered to such address (evidenced, in the case
of delivery by overnight courier, by confirmation of delivery from the overnight
courier service making such delivery, and in the case of a telecopy, by receipt
of a transmission confirmation form or the addressee's confirmation of receipt),
or (b) in the case of any notice or communication sent by mail, three business
days after being sent, if sent by registered or certified mail, with first-class
postage prepaid. Each of the parties hereto shall be entitled to specify a
different address by giving notice as aforesaid to each of the other parties
hereto.
<PAGE>
                                                                 Page 222 of 229

         SECTION 5.09 GOVERNING LAW. This Agreement shall be governed by and
construed in accordance with the domestic substantive law of the State of New
York, without giving effect to any choice or conflict of law provision or rule
that would cause the application of the law of any other jurisdiction.

         SECTION 5.10 TERMINATION. This Agreement will terminate at the end of
the Term or earlier upon the written approval of the Company and Two-Thirds in
Interest of the Purchasers.

         SECTION 5.11 FIDUCIARY DUTIES. Notwithstanding the restrictions set
forth herein, any director of the Company may exercise his fiduciary duties in
his capacity as a director with respect to the Company, as opposed to taking
action with respect to the direct or indirect ownership of any Voting Stock, and
no such exercise of fiduciary duties shall be deemed to be a breach of or a
violation of the restrictions set forth herein, and none of the Purchasers shall
have any liability hereunder for any such exercise of fiduciary duties by such
director in his capacity as a director of the Company.



                     [Remainder of Page Intentionally Blank]

<PAGE>
                                                                 Page 223 of 229


                                                          [Standstill Agreement]


         IN WITNESS WHEREOF, the Company and the Purchasers have caused this
Agreement to be executed as of the date first above written by their respective
officers thereunto duly authorized.



The Company:                ADVANCED RADIO TELECOM CORP.


                            By: /s/ HENRY C. HIRSCH
                            ----------------------------------------------------
                            Name: Henry C. Hirsch
                            Title: Chairman and CEO


The Purchasers:             U.S. TELESOURCE, INC.

                            By: /s/ MARC B. WEISBERG
                            ----------------------------------------------------
                            Name: Marc B. Weisberg
                            Title: President and Chief Executive Officer


                            OAK INVESTMENT PARTNERS VIII, LIMITED PARTNERSHIP

                            By:  Oak Associates VIII, LLC, General Partner

                            /s/ BANDEL L. CARANO
                            ----------------------------------------------------
                            By:  Bandel L. Carano, Managing Member


                            OAK VIII AFFILIATE FUND, LIMITED PARTNERSHIP

                            By:  Oak VIII Affiliates, LLC, General Partner

                            /s/ BRANDEL L. CARANO
                            ----------------------------------------------------
                            By:  Bandel L. Carano, Managing Member
<PAGE>
                                                                 Page 224 of 229

                                                          [Standstill Agreement]

                                   MERITECH CAPITAL AFFILIATES L.P.

                                   By:  MeriTech Capital Associates, L.L.C.
                                        its General Partner

                                   By:  MeriTech Management L.L.C.
                                        a managing member

                                   By: /s/ PAUL MADERA
                                       -----------------------------------------
                                       Paul Madera, a managing member


                                   MERITECH CAPITAL PARTNERS L.P.

                                   By:  MeriTech Capital Associates L.L.C.
                                        its General Partner

                                   By:  MeriTech Management L.L.C.
                                        a managing member

                                   By: /s/ PAUL MADERA
                                       -----------------------------------------
                                       Paul Madera, a managing member

<PAGE>
                                                                 Page 225 of 229

                                                          [Standstill Agreement]

                               ACCEL VI L.P.
                               BY:  ACCEL VI ASSOCIATES L.L.C.
                               ITS GENERAL PARTNER

                               By: /s/ G. CARTER SEDNAOUI
                                   ---------------------------------------------
                                   Managing Member


                               ACCEL INTERNET FUND II L.P.
                               BY:  ACCEL INTERNET FUND II ASSOCIATES L.L.C.
                               ITS GENERAL PARTNER

                               By:  /s/ G. CARTER SEDNAOUI
                                   ---------------------------------------------
                                   Managing Member


                               ACCEL KEIRETSU VI L.P.
                               By:  ACCEL KEIRETSU VI ASSOCIATES L.L.C.
                               ITS GENERAL PARTNER

                               By:  /s/ G. CARTER SEDNAOUI
                                   ---------------------------------------------
                                   Managing Member


                               ACCEL INVESTORS '98 L.P.

                               By:  /s/ G. CARTER SEDNAOUI
                                   ---------------------------------------------
                                   General Partner


<PAGE>
                                                                 Page 226 of 229

                                                          [Standstill Agreement]

                                       BRENTWOOD ASSOCIATES IV, L.P.

                                       By:  Brentwood IX Ventures, L.L.C.
                                       Its General Partners

                                       By: /s/ JOHN L. WALECKA
                                           -------------------------------------
                                           Name:  John L. Walecka
                                           Title:  Managing Member


                                       BRENTWOOD AFFILIATES FUND IX, L.P.

                                       By:  Brentwood IX Ventures, L.L.C.
                                       Its General Partner

                                       By: /s/ JOHN L. WALECKA
                                           -------------------------------------
                                           Name:  John L. Walecka
                                           Title:  Managing Member

<PAGE>
                                                                 Page 229 of 229

                                                          [Standstill Agreement]


                              WORLDVIEW TECHNOLOGY PARTNERS II, L.P.
                              By: Worldview Capital II, L.P., General Partner
                              By: Worldview Equity I, L.L.C., General Partner

                              By: /s/ JAMES WEI
                                  -------------------------------------------
                                  Name:  James Wei
                                  Title:  Member

                         WORLDVIEW TECHNOLOGY INTERNATIONAL II, L.P.
                         By:   Worldview Capital II, L.P., General Partner
                         By:   Worldview Equity I, L.L.C., General Partner

                         By:  /s/ JAMES WEI
                              --------------------------------------------------
                              Name:  James Wei
                              Title:  Member

                         WORLDVIEW STRATEGIC PARTNERS II, L.P.
                         By:   Worldview Capital II, L.P., General Partner
                         By:   Worldview Equity I, L.L.C., General Partner

                         By:  /s/ JAMES WEI
                              --------------------------------------------------
                              Name:  James Wei
                              Title:  Member

<PAGE>
                                                                 Page 228 of 229

                                                          [Standstill Agreement]


                              BESSEMER VENTURE PARTNERS IV L.P.
                              By:   Deer IV & Co. LLC, General Partner

                              By:  /s/ ROBERT H. BUESCHER
                                   ---------------------------------------------
                                   Name:  Robert H. Buescher
                                   Title:  Manager

                              BESSEC VENTURES IV L.P.
                              By:   Deer IV & Co. LLC, General Partner

                              By:  /s/ ROBERT H. BUESCHER
                                   ---------------------------------------------
                                   Name:  Robert H. Buescher
                                   Title:  Manager

                              COVE VENTURES, LLC
                              By:   Cove Road Associates, LLC, Managing Member

                              By:  /s/ ROBERT GOODMAN
                                   ---------------------------------------------
                                   Name:  Robert Goodman
                                   Title:  Managing Member
<PAGE>
                                                                 Page 229 of 229

                                                          [Standstill Agreement]

                            ADAMS CAPITAL MANAGEMENT, L.P.
                            By:   ACM Capital Partners II, L.P., General Partner
                            By:   Joel P. Adams, General Partner

                            By:  /s/ JOEL P. ADAMS
                                 -----------------------------------------------
                                 Name:  Joel P. Adams
                                 Title:  General Partner



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