CROWN CASTLE INTERNATIONAL CORP
SC 13D/A, 1999-11-09
COMMUNICATIONS SERVICES, NEC
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<PAGE>

                                 UNITED STATES
                      SECURITIES AND EXCHANGE COMMISSION
                            Washington, D.C. 20549

                                Amendment No. 1
                                      to
                                 SCHEDULE 13D

                   Under the Securities Exchange Act of 1934
                              (Amendment No. 1)*

                       Crown Castle International Corp.
                       --------------------------------
                               (Name of Issuer)

                    Common Stock, Par Value $0.01 Per Share
                    ---------------------------------------
                        (Title of Class of Securities)

                                   228227104
                       --------------------------------
                                (CUSIP Number)

                               David V. Smalley
                             Debevoise & Plimpton
                        International Financial Centre
                               Old Broad Street
                                London EC2N 1HQ
                                United Kingdom
                            (011)(44)(171) 786-9000
                            -----------------------
(Name, Address and Telephone Number of Person Authorized to Receive Notices and
                                Communications)

                        September 28 - October 25, 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 which is the subject of this Schedule 13D, and is filing this
schedule because of (S)(S) 240.13d-1(3), 240.13d-1(f) or 240.13d-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 (S) 240.13d-7(b) for other
parties to whom copies are to be sent.

* The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter
disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed
to be "filed" for the purposes of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).

                      (Continued on the following pages)
<PAGE>

- ------------------------------------------------------------------------------
      NAME OF REPORTING PERSON
 1    S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

      Candover Investments plc
- ------------------------------------------------------------------------------
      CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
 2                                                              (a) [_]
                                                                (b) [x]
- ------------------------------------------------------------------------------
      SEC USE ONLY
 3

- ------------------------------------------------------------------------------
      SOURCE OF FUNDS
 4
      N.A.
- ------------------------------------------------------------------------------
      CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
      TO ITEMS 2(d) or 2(e) [_]
 5
- ------------------------------------------------------------------------------
      CITIZENSHIP OR PLACE OF ORGANIZATION
 6
      England
- ------------------------------------------------------------------------------
                          SOLE VOTING POWER
                     7
     NUMBER OF
                             8,953,300
      SHARES       -----------------------------------------------------------
                          SHARED VOTING POWER
   BENEFICIALLY      8

     OWNED BY                    0
                   -----------------------------------------------------------
       EACH               SOLE DISPOSITIVE POWER
                     9
    REPORTING
                            8,953,300
      PERSON       -----------------------------------------------------------
                          SHARED DISPOSITIVE POWER
       WITH          10
                                 0
- ------------------------------------------------------------------------------
      AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
11
      81,903,623 (Includes all Shares beneficially owned by persons reporting
      on the Original Schedule 13D)
- ------------------------------------------------------------------------------
      CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES
12
                                                                          [_]
- ------------------------------------------------------------------------------
      PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
13
                  56.52%
- ------------------------------------------------------------------------------
      TYPE OF REPORTING PERSON
14
      IV
- ------------------------------------------------------------------------------

                                       2
<PAGE>

- ------------------------------------------------------------------------------
      NAME OF REPORTING PERSON
 1    S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

      Candover (Trustees) Limited
- ------------------------------------------------------------------------------
      CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
 2                                                              (a) [_]
                                                                (b) [x]
- ------------------------------------------------------------------------------
      SEC USE ONLY
 3

- ------------------------------------------------------------------------------
      SOURCE OF FUNDS
 4
      N.A.
- ------------------------------------------------------------------------------
      CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
      TO ITEMS 2(d) or 2(e) [_]
 5
- ------------------------------------------------------------------------------
      CITIZENSHIP OR PLACE OF ORGANIZATION
 6
     England
- ------------------------------------------------------------------------------
                          SOLE VOTING POWER
                     7
     NUMBER OF
                             164,583
      SHARES       -----------------------------------------------------------
                          SHARED VOTING POWER
   BENEFICIALLY      8

     OWNED BY                    0
                   -----------------------------------------------------------
       EACH               SOLE DISPOSITIVE POWER
                     9
    REPORTING
                         164,583
      PERSON       -----------------------------------------------------------
                          SHARED DISPOSITIVE POWER
       WITH          10
                                0
- ------------------------------------------------------------------------------
      AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
11
      81,903,623 (Includes all Shares beneficially owned by persons reporting
      on the Original Schedule 13D)
- ------------------------------------------------------------------------------
      CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES
12
                                                                          [_]
- ------------------------------------------------------------------------------
      PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
13
                  56.52%
- ------------------------------------------------------------------------------
      TYPE OF REPORTING PERSON
14
      IV
- ------------------------------------------------------------------------------

                                       3
<PAGE>

- ------------------------------------------------------------------------------
      NAME OF REPORTING PERSON
 1    S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

      Candover Partners Limited (as general partner of the Candover 1994 UK
      Limited Partnership, the Candover 1994 UK No. 2 Limited Partnership, the
      Candover 1994 US No. 1 Limited Partnership and the Candover 1994 US No. 2
      Limited Partnership)
- ------------------------------------------------------------------------------
      CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
 2                                                              (a) [_]
                                                                (b) [x]
- ------------------------------------------------------------------------------
      SEC USE ONLY
 3

- ------------------------------------------------------------------------------
      SOURCE OF FUNDS
 4
      N.A.
- ------------------------------------------------------------------------------
      CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
      TO ITEMS 2(d) or 2(e) [_]
 5
- ------------------------------------------------------------------------------
      CITIZENSHIP OR PLACE OF ORGANIZATION
 6
      England
- ------------------------------------------------------------------------------
                          SOLE VOTING POWER
                     7
     NUMBER OF
                             6,948,092
      SHARES       -----------------------------------------------------------
                          SHARED VOTING POWER
   BENEFICIALLY      8

     OWNED BY                    0
                   -----------------------------------------------------------
       EACH               SOLE DISPOSITIVE POWER
                     9
    REPORTING
                         6,948,092
      PERSON       -----------------------------------------------------------
                          SHARED DISPOSITIVE POWER
       WITH          10
                                 0
- ------------------------------------------------------------------------------
      AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
11
      81,903,623 (Includes all Shares beneficially owned by persons reporting
      on the Original Schedule 13D)
- ------------------------------------------------------------------------------
      CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES
12
                                                                          [_]
- ------------------------------------------------------------------------------
      PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
13
                  56.52%
- ------------------------------------------------------------------------------
      TYPE OF REPORTING PERSON
14
      IV
- ------------------------------------------------------------------------------

                                       4
<PAGE>

- ------------------------------------------------------------------------------
      NAME OF REPORTING PERSON
 1    S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

      Candover Services Limited
- ------------------------------------------------------------------------------
      CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
 2                                                              (a) [_]
                                                                (b) [x]
- ------------------------------------------------------------------------------
      SEC USE ONLY
 3

- ------------------------------------------------------------------------------
      SOURCE OF FUNDS
 4
      N.A.
- ------------------------------------------------------------------------------
      CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
      TO ITEMS 2(d) or 2(e) [_]
 5
- ------------------------------------------------------------------------------
      CITIZENSHIP OR PLACE OF ORGANIZATION
 6
      England
- ------------------------------------------------------------------------------
                          SOLE VOTING POWER
                     7
     NUMBER OF
                             6,948,092
      SHARES       -----------------------------------------------------------
                          SHARED VOTING POWER
   BENEFICIALLY      8

     OWNED BY                    0
                   -----------------------------------------------------------
       EACH               SOLE DISPOSITIVE POWER
                     9
    REPORTING
                         6,948,092
      PERSON       -----------------------------------------------------------
                          SHARED DISPOSITIVE POWER
       WITH          10
                                 0
- ------------------------------------------------------------------------------
      AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
11
      81,903,623 (Includes all Sharees beneficially owned by persons reporting
      on the Original Schedule 13D)
- ------------------------------------------------------------------------------
      CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES
12
                                                                           [_]
- ------------------------------------------------------------------------------
      PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
13
                 56.52%
- ------------------------------------------------------------------------------
      TYPE OF REPORTING PERSON
14
      IV
- ------------------------------------------------------------------------------

                                       5
<PAGE>

                 Amendment No.1 to a Statement on Schedule 13D

          This Amendment No.1 amends the Statement on Schedule 13D relating to
the common stock, par value $.01 per share (the "Shares"), of Crown Castle
                                                 ------
International Corp., a Delaware corporation (the "Company") filed with the
                                                  -------
Securities and Exchange Commission (the "Commission") on September 1, 1998 (the
                                         ----------
"Original Schedule 13D").  This Statement is being filed on behalf of the
- ----------------------
reporting persons (each a "Candover Reporting Person," and collectively the
                           -------------------------
"Candover Reporting Persons") identified on the cover pages of this Amendment
- ---------------------------
No. 1.  Information in respect of each Candover Reporting Person is given solely
by such Candover Reporting Person and no Candover Reporting Person has
responsibility for the accuracy or completeness of information supplied by any
other Candover Reporting Person.

Item 1.   Security and Issuer.

This Item is not amended.

Item 2.   Identity and Background.

This Item is amended only to the following extent:

     The paragraph headed "Candover Partners Limited (as general partner of the
                           ----------------------------------------------------
     Candover 1994 UK Limited Partnership, the Candover 1994 UK No.2 Limited
     -----------------------------------------------------------------------
     Partnership, the Candover 1994 US No.1 Limited Partnership and the
     ------------------------------------------------------------------
     Candover 1994 US No.2 Limited Partnership)" is deleted and replaced with
     ------------------------------------------
     the following paragraph:

     "Candover Partners Limited (as general partner of the Candover 1994 UK
      ---------------------------------------------------------------------
     Limited Partnership, the Candover 1994 UK No.2 Limited Partnership, the
     -----------------------------------------------------------------------
     Candover 1994 US No.1 Limited Partnership and the Candover 1994 US No.2
     -----------------------------------------------------------------------
     Limited Partnership)
     --------------------

               Candover Partners is an English company with its principal
     executive office located at 20 Old Bailey, London EC4M 7LN. The principal
     business of Candover Partners is to analyze and make investment decisions
     in its role as general partner of the various limited partnerships
     constituting the Candover 1989, 1991, 1994 and 1997 Funds. Candover
     Partners is regulated by the Investment Management Regulatory Organisation
     of the U.K. ("IMRO"). Candover Partners is a majority owned direct
     subsidiary of Candover Services and a wholly owned indirect subsidiary of
     Candover Investments."

                                       6
<PAGE>

Item 3.   Source and Amount of Funds or Other Consideration.

This Item is supplemented as follows:

          Over the period from September 28, 1999 to October 25, 1999, the
Candover Reporting Persons sold 2,376,900 Shares in the aggregate pursuant to
Rule 144 under the Securities Act of 1933, as amended.  The number of Shares
sold on behalf of each Candover Reporting Person is set forth in the following
table:

<TABLE>
<CAPTION>
          Seller                                     Number of Shares Sold
          ------                                     ---------------------
          <S>                                        <C>

          Candover Investments plc                           488,693
          ("Candover Investments")
            --------------------

          Candover Partners Limited                          965,259
          ("Candover Partners")
            -----------------
          (as general partner of the
          Candover 1994 UK Limited
          Partnership)

          Candover Partners                                  261,459
          (as general partner of the
          Candover 1994 UK No.2
          Limited Partnership)

          Candover Partners                                   46,824
          (as general partner of the
          Candover 1994 US No.1
          Limited Partnership)

          Candover Partners                                  570,931
          (as general partner of the
          Candover 1994 US No.2
          Limited Partnership)

          Candover (Trustees) Limited                         43,734
          ("Candover Trustees")
            -----------------
</TABLE>

          More detailed information relating to such sales, including the
average daily sale price and the number of Shares sold on a daily basis, is
attached as Schedule A hereto, which schedule is hereby incorporated into this
Item 3 by reference in its entirety.

          Form 144 notices relating to such sales were filed with the Commission
on September 28, 1999 and October 1, 1999.  See Exhibits 1 through 12 hereto.
Sales were made on Nasdaq through Lehman Brothers, Inc. ("Lehman Brothers"), a
                                                          ---------------
registered broker under the Securities Exchange Act of 1934, as amended (the
"Exchange Act").  Sales made in September were reported on a Form 4, filed with
- -------------

                                       7
<PAGE>

the Commission on October 7, 1999.  See Exhibit 13 hereto.  Sales made in
October were reported on a Form 4, filed with the Commission on November 1,
1999.  See Exhibit 14 hereto.

Item 4.   Purpose of Transaction.

This Item is supplemented as follows:

          The purposes of the sales by the Candover Reporting Persons described
in Item 3 above were to diversify the equity holdings of the Candover
Reporting Persons and to realize part of the value of the investment in the
Shares for the benefit of the investors in the partnerships on whose behalf
Candover Partners made sales.

          Additional sales may be made in the future for such purposes or for
other purposes.  Although each of the Candover Reporting Persons believes that
the Shares that it beneficially owns are an attractive investment, each of the
Candover Reporting Persons on an individual basis continues to monitor and
evaluate its investment in the Company in light of pertinent factors, including
without limitation the following: (i) the Company's business, operations,
                                   -
assets, financial condition and prospects; (ii) market, general economic and
                                            --
other conditions; and (iii) other investment opportunities available to one or
                       ---
more of the Candover Reporting Persons.  Candover Partners also monitors and
evaluates the Shares it holds in light of its obligations as the general partner
of the Candover 1994 UK Limited Partnership, the Candover 1994 UK No.2 Limited
Partnership, the Candover 1994 US No.1 Limited Partnership and the Candover 1994
US No.2 Limited Partnership (collectively the "Candover Partnerships").
                                               ---------------------
Candover Trustees also monitors and evaluates the Shares it holds in light of
its obligations as the trustee of the Candover Staff Co-Investment Scheme.

          In light of the foregoing factors, and the plans and requirements of
the Candover Reporting Persons from time to time, some or all of the Candover
Reporting Persons may decide to: (i) dispose of some or all of the securities of
                                  -
the Company which they beneficially own; or (ii) acquire additional securities
                                             --
of the Company.  The Candover Reporting Persons reserve the right, either
individually or in any combination among themselves or together with one or more
stockholders of the Company, to decide in the future to take or cause to be
taken one or more of the foregoing actions.  There can be no assurance that any
of the foregoing transactions will occur or as to the timing of any such
transactions.

          Except as set forth above, none of the Candover Reporting Persons has
plans or proposals with respect to any of the matters set forth in paragraphs
(a) through (j) of Item 4 of Schedule 13D.

          The Candover Reporting Persons disclaim that they are part of a group
(as such term is set forth in Rule 13(d) under the Exchange Act).  Additionally,
each Candover Reporting Person disclaims beneficial ownership of all Shares
which are not directly owned of record by such Candover Reporting Person.

                                       8
<PAGE>

Item 5.   Interest in Securities of the Issuer.

This Item is supplemented and amended as follows:

          In accordance with Rule 13d-5(b)(1) under the Exchange Act and by
virtue of the Stockholders Agreement discussed in Item 6 of the Original
Schedule 13D (subject to the disclaimer in Item 4 of the Original Schedule 13D
and this Amendment No.1), each of the Candover Reporting Persons may be deemed
to own 81,903,623 Shares, which constitute approximately 56.52% of the
144,915,296 Shares deemed outstanding as of November 3, 1999.  The amount deemed
owned constitutes the number of Shares in which the reporting persons that filed
the Original Schedule 13D are interested or deemed interested.

          The information contained in Item 3 of this Amendment No.1 is hereby
incorporated into this Item 5 by reference in its entirety.

Candover Investments plc
- ------------------------

          Candover Investments has sole voting power with respect to 8,953,300
Shares and has sole dispositive power with respect to 8,953,300 Shares.
Candover Investments is the direct beneficial owner of 1,840,625 Shares over
which it has sole voting and dispositive power.  By virtue of the relationships
reported under Item 2 of the Original Schedule 13D, Candover Investments may be
deemed to have indirect beneficial ownership of the Shares beneficially owned by
Candover Trustees and Candover Partners.

Candover (Trustees) Limited
- ---------------------------

          Candover Trustees has sole voting power with respect to 164,583 Shares
and has sole dispositive power with respect to 164,583 Shares.  Candover
Trustees is the direct beneficial owner of 164,583 Shares over which it has sole
voting and dispositive power.

Candover Partners Limited (as general partner of the Candover 1994 UK Limited
- -----------------------------------------------------------------------------
Partnership, the Candover 1994 UK No.2 Limited Partnership, the Candover 1994 US
- --------------------------------------------------------------------------------
No.1 Limited Partnership and the Candover 1994 US No.2 Limited Partnership).
- ---------------------------------------------------------------------------

          Candover Partners has sole voting power with respect to 6,948,092
Shares and has sole dispositive power with respect to 6,948,092 Shares.
Candover Partners is the direct beneficial owner of 6,948,092 Shares over which
it has sole voting and dispositive power.

Candover Services Limited
- -------------------------

          Candover Services has sole voting power with respect to 6,948,092
Shares and has sole dispositive power with respect to 6,948,092 Shares.  By
virtue of the relationships reported under Item 2

                                       9
<PAGE>

of the Original Schedule 13D, Candover Services may be deemed to have indirect
beneficial ownership of the Shares beneficially owned by Candover Partners.

Item 6.   Contracts, Arrangements, Understandings or Relationships With Respect
          to Securities of the Issuer

This Item is supplemented as follows:

          As discussed in Item 3 of this Amendment No.1, the Candover Reporting
Persons sold Shares through Lehman Brothers.  The relationship between the
Candover Reporting Persons and Lehman Brothers is governed by a standard Lehman
Brothers Corporate Client Agreement.

          The Stockholders Agreement described in Item 6 of the Original
Schedule 13D (the "Stockholders Agreement") has subsequently been amended.
                   ----------------------
Copies of the amendments are attached hereto as Exhibits 15 through 18 and the
description of the Stockholders Agreement contained herein is qualified in its
entirety by reference to such Exhibits, each of which are hereby incorporated
herein by reference in its entirety.

          Amendment Number One to the Stockholders Agreement provided that
Candover Investments, Candover Partners (as general partner of the Candover
Partnerships) and Candover Trustees would lose their tag-along rights and cease
to be subject to the voting provisions under the Stockholders Agreement upon a
disposition of Shares by any such party to any of its limited partners.
Amendment Number Two related to the use of the "Crown" name by the Company.
Amendment Number Three provided that certain parties to the Stockholders
Agreement lost their tag-along rights and registration rights in connection with
a "DECS transaction."  This transaction was the subject of a Registration
Statement filed by the Company on Form S-3 (Reg. No. 333-83395) and a
Registration Statement filed by DECS Trust V on Form N-2 (Reg. No. 333-83965).
Amendment Number Four provided that Shares distributed by a party to the
Stockholders Agreement to their equityholders shall cease to be subject to the
Stockholders Agreement and that such equityholders will not become party to the
Stockholders Agreement.

Item 7.   Material to Be Filed as Exhibits.

Exhibit 1      Form 144 filed with the Commission on September 28, 1999 by
               Candover Partners as general partner of the Candover 1994 UK
               Limited Partnership.

Exhibit 2      Form 144 filed with the Commission on September 28, 1999 by
               Candover Partners as general partner of the Candover 1994 UK No.2
               Limited Partnership.

Exhibit 3      Form 144 filed with the Commission on September 28, 1999 by
               Candover Partners as general partner of the Candover 1994 US No.1
               Limited Partnership.

                                       10
<PAGE>

Exhibit 4      Form 144 filed with the Commission on September 28, 1999 by
               Candover Partners as general partner of the Candover 1994 US No.2
               Limited Partnership.

Exhibit 5      Form 144 filed with the Commission on September 28, 1999 by
               Candover Trustees.

Exhibit 6      Form 144 filed with the Commission on September 28, 1999 by
               Candover Investments.

Exhibit 7      Form 144 filed with the Commission on October 1, 1999 by Candover
               Partners as general partner of the Candover 1994 UK Limited
               Partnership.

Exhibit 8      Form 144 filed with the Commission on October 1, 1999 by Candover
               Partners as general partner of the Candover 1994 UK No.2 Limited
               Partnership.

Exhibit 9      Form 144 filed with the Commission on October 1, 1999 by
               Candover Partners as general partner of the Candover 1994 US No.1
               Limited Partnership.

Exhibit 10     Form 144 filed with the Commission on October 1, 1999 by
               Candover Partners as general partner of the Candover 1994 US No.2
               Limited Partnership.

Exhibit 11     Form 144 filed with the Commission on October 1, 1999 by
               Candover Trustees.

Exhibit 12     Form 144 filed with the Commission on October 1, 1999 by
               Candover Investments.

Exhibit 13     Form 4 filed with the Commission on October 7, 1999 by Candover
               Investments, Candover Partners, Candover Partners as general
               partner of the Candover Partnerships, Candover Trustees and
               Candover Services.

Exhibit 14     Form 4 filed with the Commission on November 1, 1999 by Candover
               Investments, Candover Partners, Candover Partners as general
               partner of the Candover Partnerships, Candover Trustees and
               Candover Services.

Exhibit 15     Amendment, dated as of November 12, 1998, to the Stockholders
               Agreement, dated as of August 21, 1999, among Crown Castle
               International Corp. (formerly named Castle Tower Holding Corp.)
               ("CCIC") and each of the stockholders of CCIC listed on Schedule
                 ----
               1 to the Stockholders Agreement.

Exhibit 16     Amendment Number Two to Stockholders Agreement, dated effective
               May 24, 1999, among CCIC and each of the stockholders of CCIC
               listed on Schedule 1 to the Stockholders Agreement.

                                       11
<PAGE>

Exhibit 17     Amendment Number Three to Stockholders Agreement, dated as of
               August 11, 1999, among CCIC and each of the stockholders of CCIC
               listed on Schedule 1 to the Stockholders Agreement.

Exhibit 18     Amendment Number Four to Stockholders Agreement, dated effective
               October 1, 1999, among CCIC and each of the stockholders of CCIC
               listed on Schedule 1 to the Stockholders Agreement.

Exhibit 19     Joint Filing Agreement, dated November 3, 1999, among Candover
               Investments plc, Candover (Trustees) Limited, Candover Partners
               Limited and Candover Services Limited.

                                       12
<PAGE>

                                   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.

Date: November 3, 1999

                           CANDOVER INVESTMENTS PLC

                           By:  /s/ P.R. Neal
                              ----------------------------------
                              Name: P.R. Neal
                              Title: Company Secretary
<PAGE>

                                   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.

Date: November 3, 1999

                                       CANDOVER (TRUSTEES) LIMITED

                                       By: /s/ P.R. Neal
                                          ----------------------------
                                          Name:  P.R. Neal
                                          Title: Company Secretary

<PAGE>

                                   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.


Date: November 3, 1999


                                  CANDOVER PARTNERS LIMITED
                                  (as general partner of the Candover 1994 UK
                                  Limited Partnership, the Candover 1994 UK
                                  No. 2 Limited Partnership, the Candover 1994
                                  US No. 1 Limited Partnership and the Candover
                                  1994 US No. 2 Limited Partnership)

                                  By: /s/ P.R. Neal
                                     -----------------------------------
                                     Name:  P.R. Neal
                                     Title: Company Secretary
<PAGE>

                                   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.



Date: November 3, 1999


                                            CANDOVER SERVICES LIMITED

                                            By:/s/ P.R. Neal
                                               ---------------------------------
                                               Name: P.R. Neal
                                               Ttile: Company Secretary




<PAGE>


                                                                      Schedule A

<TABLE>
<CAPTION>

- -----------------------------------------------------------------------------------------------------------------
CCIC Sale Programme - 1999
- -----------------------------------------------------------------------------------------------------------------
                               Candover Investments plc                    Candover Trustees Ltd
                               ------------------------                    ---------------------
           Sale      No. of                                        No. of
          price     Shares       Gross        SEC         Net      Shares        Gross      SEC        Net
Date     per share    Sold      Proceeds      Fee       Amount      Sold        Proceeds    Fee       Amount
           US$                    US$         US$        US$                      US$       US$        US$
- -----------------------------------------------------------------------------------------------------------------
 <S>       <C>       <C>     <C>          <C>      <C>            <C>     <C>           <C>        <C>
28/09/99   18.6875     2,056    38,421.50    -1.28     38,420.22      184       3,438.50   -0.11      3,438.39
28/09/99   18.6875    15,420   288,161.25    -9.61    288,151.64    1,380      25,788.75   -0.86     25,787.89
30/09/99   18.3990   123,360 2,269,700.64   -75.66  2,269,624.98   11,040     203,124.96   -6.77    203,118.19
 1/10/99   18.5000    30,840   570,540.00   -19.02    570,520.98    2,760      51,060.00   -1.70     51,058.30
 4/10/99   18.5192    53,456   989,962.36   -33.00    989,929.36    4,784      88,595.85   -2.95     88,592.90
 5/10/99   18.1875    92,520 1,682,707.50   -56.09  1,682,651.41    8,280     150,592.50   -5.02    150,587.48
 7/10/99   18.6458    21,589   402,544.18   -13.42    402,530.76    1,932      36,023.69   -1.20     36,022.49
 8/10/99   18.5625    10,280   190,822.50    -6.36    190,816.14      920      17,077.50   -0.57     17,076.93
11/10/99   18.6447    19,532   364,168.28   -12.14    364,156.14    1,748      32,590.94   -1.09     32,589.85
12/10/99   18.6875     2,056    38,421.50    -1.28     38,420.22      184       3,438.50   -0.11      3,438.39
20/10/99   18.0337    26,728   482,004.73   -16.07    481,988.66    2,392      43,136.61   -1.44     43,135.17
21/10/99   18.0000     3,084    55,512.00    -1.85     55,510.15      276       4,968.00   -0.17      4,967.83
22/10/99   18.3254    69,904 1,281,018.76   -42.70  1,280,976.06    6,256     114,643.70   -3.82    114,639.88
25/10/99   18.1358    17,868   324,050.47   -10.80    324,039.67    1,598      28,981.01   -0.97     28,980.04

shrs in sale
program              488,701                                       43,736
                     -------                                      -------
shrs left to go            8                                            2
                     -------                                      -------
- -----------------------------------------------------------------------------------------------------------------
Total sales:         488,693 8,978,035.67  -299.28  8,977,736.39   43,734     803,460.51  -26.78    803,433.73
=================================================================================================================
Original Holdings  2,329,318                                      208,317
- ----------------------------------------------------------------------------------------------------------------
No. of shares held
after sales:       1,840,625                                      164,583
================================================================================================================
- ----------------------------------------------------------------------------------------------------------------
</TABLE>





<TABLE>
<CAPTION>

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

- --------------------------------------------------------------------------------------------------------------
                               1994 UK LP                                 1994 UK. No. 2 L.P.
                               ----------                                 -------------------
           Sale      No. of                                        No. of
          price     Shares      Gross         SEC         Net      Shares       Gross      SEC         Net
Date     per share    Sold     Proceeds       Fee        Amount     Sold      Proceeds     Fee       Amount
           US$                   US$          US$         US$                    US$       US$         US$
- --------------------------------------------------------------------------------------------------------------
<S>       <C>      <C>      <C>           <C>       <C>           <C>     <C>           <C>        <C>
28/09/99   18.6875    4,061     75,889.94    -2.53      75,887.41    1,100     20,556.25   -0.69     20,555.56
28/09/99   16.6875   30,457    569,165.19   -18.97     569,146.22    8,250    154,171.88   -5.14    154,166.74
30/09/99   18.3990  243,660  4,483,100.34  -149.44   4,482,950.90   66,000  1,214,334.00  -40.48  1,214,293.52
 1/10/99   18.5000   60,915  1,126,927.50   -37.56   1,126,889.94   16,500    305,250.00  -10.18    305,239.82
 4/10/99   18.5192  105,586  1,955,368.25   -65.18   1,955,303.07   28,600    529,649.12  -17.65    529,631.47
 5/10/99   18.1875  182,745  3,323,674.69  -110.79   3,323,563.90   49,500    900,281.25  -30.01    900,251.24
 7/10/99   18.6458   42,640    795,056.91   -26.50     795,030.41   11,550    215,358.99   -7.18    215,351.81
 8/10/99   18.5625   20,305    376,911.56   -12.56     376,899.00    5,500    102,093.75   -3.40    102,090.35
 11/10/99  18.6447   38,579    719,293.88   -23.98     719,269.90   10,450    194,837.12   -6.49    194,830.63
 12/10/99  18.6875    4,061     75,889.94    -2.53      75,887.41    1,100     20,556.25   -0.69     20,555.56
 20/10/99  18.0337   52,793    952,053.12   -31.74     952,021.38   14,300    257,881.91   -8.60    257,873.31
 21/10/99  18.0000    6,091    109,638.00    -3.65     109,634.35    1,650     29,700.00   -0.99     29,699.01
 22/10/99  18.3254  138,074  2,530,261.28   -84.34   2,530,176.94   37,400    685,369.96  -22.85    685,347.11
 25/10/99  18.1358   35,292    640,048.65   -21.33     640,027.32    9,559    173,360.11   -5.78    173,354.33

 shrs in sale
 program
                    965,279                                        261,465
                    -------                                        -------
 shrs left to go         20                                              6
- --------------------------------------------------------------------------------------------------------------
Total sales:        965,259 17,733,279.25  -591.10  17,732,688.15  261,459  4,803,400.58 -160.13  4,803,240.45
==============================================================================================================
Original Holdings 4,600,805                                      1,246,810
- --------------------------------------------------------------------------------------------------------------
No. of shares held
after sales:      3,635,546                                        985,351
==============================================================================================================
- --------------------------------------------------------------------------------------------------------------
</TABLE>

<PAGE>

<TABLE>
<CAPTION>

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

- ------------------------------------------------------------------------------------------------------------------------------------
          1994 US. No. 1 L.P.                        1994 US. No. 2 L.P.                                 TOTALS
          ------------------                         -------------------                                 ------
 No. of                                 No. of                                          No. of
 Shares     Gross    SEC       Net      Shares      Gross       SEC        Net          Shares      Gross       SEC       Net
   Sold    Proceeds  Fee      Amount      Sold     Proceeds     Fee       Amount          Sold    Proceeds      Fee     Amount
            US$      US$       US$                   US$        US$        US$                       US$        US$       US$
- ------------------------------------------------------------------------------------------------------------------------------------
<S>     <C>         <C>   <C>         <C>      <C>            <C>     <C>           <C>        <C>            <C>      <C>
    197   3,681.44  -0.12   3,681.32    2,402      44,887.38   -1.50     44,885.88     10,000     186,875.00     -6.23    186,868.77
  1,478  27,620.13  -0.92  27,619.21   18,015     336,655.31  -11.22    336,644.09     75,000   1,401,562.50    -46.72  1,401,515.78
 11,820 217,476.18  -7.25 217,468.93  144,120   2,651,663.88  -88.39  2,651,575.49    600,000  11,039,400.00   -367.99 11,039,032.01
  2,955  54,667.50  -1.82  54,665.68   36,030     666,555.00  -22.22    666,532.78    150,000   2,775,000.00    -92.50  2,774,907.50
  5,122  94,855.34  -3.16  94,852.18   62,452   1,156,561.08  -38.55  1,156,522.53    260,000   4,814,992.00   -160.49  4,814,831.51
  8,865 161,232.19  -5.37 161,226.82  108,090   1,965,886.88  -65.53  1,965,821.35    450,000   8,184,375.00   -272.81  8,184,102.19
  2,068  38,559.51  -1.29  38,558.22   25,221     470,265.72  -15.68    470,250.04    105,000   1,957,809.00    -65.27  1,957,743.73
    985  18,284.06  -0.61  18,283.45   12,010     222,935.63   -7.43    222,928.20     50,000     928,125.00    -30.93    928,094.07
  1,872  34,902.88  -1.16  34,901.72   22,819     425,453.41  -14.18    425,439.23     95,000   1,771,246.50    -59.04  1,771,187.46
    197   3,681.44  -0.12   3,681.32    2,402      44,887.38   -1.50     44,885.88     10,000     186,875.00     -6.23    186,868.77
  2,561  46,184.31  -1.54  46,182.77   31,226     563,120.32  -18.77    563,101.55    130,000   2,344,381.00    -78.16  2,344,302.84
    296   5,328.00  -0.18   5,327.82    3,603      64,854.00   -2.16     64,851.84     15,000     270,000.00     -9.00    269,991.00
  6,698 122,743.53  -4.09 122,739.44   81,668   1,496,598.77  -49.89  1,496,548.88    340,000   6,230,636.00   -207.69  6,230,428.31
  1,710  31,012.22  -1.03  31,011.19   20,873     378,548.55  -12.62    378,535.93     86,900   1,576,001.02    -52.53  1,575,948.49


 46,826                               570,943                                       2,376,950
- -------                               -------                                       ---------
      2                                    12                                              50
- -------                               -------                                       ---------
- ------------------------------------------------------------------------------------------------------------------------------------
 46,824 860,228.72 -28.66 860,200.06  570,931 10,488,873.29  -349.64 10,488,523.65  2,376,900  43,667,278.02 -1,455.59 43,665,822.43
====================================================================================================================================
223,305                             2,721,645                                      11,330,200
- ------------------------------------------------------------------------------------------------------------------------------------
176,481                             2,150,714                                       8,953,300
====================================================================================================================================
- ------------------------------------------------------------------------------------------------------------------------------------

</TABLE>
<PAGE>

                                 EXHIBIT INDEX
                                 -------------

Exhibit No.                       Description
- -----------                       -----------

     1         Form 144 filed with the Commission on September 28, 1999 by
               Candover Partners as general partner of the Candover 1994 UK
               Limited Partnership is incorporated herein by reference.

     2         Form 144 filed with the Commission on September 28, 1999 by
               Candover Partners as general partner of the Candover 1994 UK No.2
               Limited Partnership is incorporated herein by reference.

     3         Form 144 filed with the Commission on September 28, 1999 by
               Candover Partners as general partner of the Candover 1994 US No.1
               Limited Partnership is incorporated herein by reference.

     4         Form 144 filed with the Commission on September 28, 1999 by
               Candover Partners as general partner of the Candover 1994 US No.2
               Limited Partnership is incorporated herein by reference.

     5         Form 144 filed with the Commission on September 28, 1999 by
               Candover Trustees is incorporated herein by reference.

     6         Form 144 filed with the Commission on September 28, 1999 by
               Candover Investments is incorporated herein by reference.

     7         Form 144 filed with the Commission on October 1, 1999 by Candover
               Partners as general partner of the Candover 1994 UK Limited
               Partnership is incorporated herein by reference.

     8         Form 144 filed with the Commission on October 1, 1999 by Candover
               Partners as general partner of the Candover 1994 UK No.2 Limited
               Partnership is incorporated herein by reference.

     9         Form 144 filed with the Commission on October 1, 1999 by Candover
               Partners as general partner of the Candover 1994 US No.1 Limited
               Partnership is incorporated herein by reference.

     10        Form 144 filed with the Commission on October 1, 1999 by Candover
               Partners as general partner of the Candover 1994 US No.2 Limited
               Partnership is incorporated herein by reference.


<PAGE>

     11        Form 144 filed with the Commission on October 1, 1999 by Candover
               Trustees is incorporated herein by reference.

     12        Form 144 filed with the Commission on October 1, 1999 by Candover
               Investments is incorporated herein by reference.

     13        Form 4 filed with the Commission on October 7, 1999 by Candover
               Investments, Candover Partners, Candover Partners as general
               partner of the Candover Partnerships, Candover Trustees and
               Candover Services is incorporated herein by reference.

     14        Form 4 filed with the Commission on November 1, 1999 by Candover
               Investments, Candover Partners, Candover Partners as general
               partner of the Candover Partnerships, Candover Trustees and
               Candover Services is incorporated herein by reference.

     15        Amendment, dated as of November 12, 1998, to the Stockholders
               Agreement, dated as of August 21, 1999, among Crown Castle
               International Corp. (formerly named Castle Tower Holding Corp.)
               ("CCIC") and each of the stockholders of CCIC listed on Schedule
                ------
               1 to the Stockholders Agreement.

     16        Amendment Number Two to Stockholders Agreement, dated effective
               May 24, 1999, among CCIC and each of the stockholders of CCIC
               listed on Schedule 1 to the Stockholders Agreement.

     17        Amendment Number Three to Stockholders Agreement, dated as of
               August 11, 1999, among CCIC and each of the stockholders of CCIC
               listed on Schedule 1 to the Stockholders Agreement.

     18        Amendment Number Four to Stockholders Agreement, dated effective
               October 1, 1999, among CCIC and each of the stockholders of CCIC
               listed on Schedule 1 to the Stockholders Agreement.

     19        Joint Filing Agreement, dated November 3, 1999, among Candover
               Investments plc, Candover (Trustees) Limited, Candover Partners
               Limited and Candover Services Limited.



<PAGE>
                                                                      Exhibit 15
                                                                      ----------


                AMENDMENT, dated as of November 12, 1998, to the Stockholders
     Agreement (the "Stockholders Agreement"), dated as of August 21,
     1998, among CROWN CASTLE INTERNATIONAL CORP. (formerly named Castle Tower
     Holding Corp.), a Delaware corporation (the "Company") and each of the
                                                  -------
     STOCKHOLDERS of the Company listed in Schedule I thereto (collectively,
     the "Stockholders" and each individually, a "Stockholder").
          ------------                            -----------

                                  WITNESSETH:

                WHEREAS, pursuant to Section 6.04 of the Stockholders Agreement,
     the Stockholders Agreement may be amended by the mutual agreement of the
     parties thereto;

                WHEREAS, the Company and the Stockholders have agreed to amend
     the Stockholders Agreement in the respects hereinafter set forth.

                NOW, THEREFORE, in consideration of the promises and the
     respective agreements hereinafter set forth and set forth in the
     Stockholders Agreement, the parties hereto agree as follows:

                SECTION 1. Amendment. Section 2.05 of the Stockholders
                           ---------
     Agreement is amended to add the following sentence at the end thereof:

          Notwithstanding the foregoing or any other provision of this
          Agreement, from and after the time immediately prior to any transfer
          of Shares by any Candover Party to any of its limited partners, no
          member of the Candover Group shall have any rights or obligations
          under Article III or V hereof with respect to any Shares.

                SECTION 2. Construction; Continuing Effect.  This agreement
                           -------------------------------
     shall be construed in connection with and as part of the Stockholders
     Agreement and each reference to the Stockholders Agreement contained in any
     other document shall mean the Stockholders Agreement as amended hereby.  As
     amended hereby, the Stockholders Agreement shall continue in full force and
     effect.

                SECTION 3. Counterparts.  This agreement may be executed in one
                           ------------
     or more counterparts, each of which shall be deemed an original but which
     together shall constitute but one instrument.  It shall not be necessary
     for each party to sign each counterpart so long as every party has signed
     at least one counterpart.
<PAGE>

            IN WITNESS WHEREOF, each party hereto has executed this
Agreement as of the day and year first above written.

                                             CROWN CASTLE
                                             INTERNATIONAL CORP.

                                             By: /s/ Kathy Broussard
                                                 -------------------------------
                                                 Name:  Kathy Broussard
                                                 Title: Vice President



<PAGE>

                                       STOCKHOLDERS:

                                       TELEDIFFUSION DE FRANCE
                                       INTERNATIONAL S.A.

                                         by /s/ Michel Azibert
                                            ------------------
                                           Name:  Michel Azibert
                                           Title: Chairman

                                       DIGITAL FUTURE INVESTMENTS B.V.,

                                         by /s/ Michel Azibert
                                            ------------------
                                           Name:  Michel Azibert
                                           Title: As Chairman of TELEDIFFUSION
                                                  DE FRANCE INTERNATIONAL S.A.
                                                  MANAGING DIRECTOR OF DFI B.V.


<PAGE>

                                  CANDOVER INVESTMENTS, PLC

                                     by  /s/ G.D. Fairservice
                                         -----------------------------
                                         Name:  G.D. FAIRSERVICE
                                         Title: DEPUTY CHIEF EXECUTIVE


                                  CANDOVER (TRUSTEES) LIMITED


                                     by  /s/ G.D. Fairservice
                                         -----------------------------
                                         Name:  G.D. FAIRSERVICE
                                         Title: DEPUTY CHIEF EXECUTIVE


                                  CANDOVER PARTNERS LIMITED
                                  (as general partner of the
                                  Candover 1994 UK Limited
                                  Partnership)


                                     by  /s/ G.D. Fairservice
                                         --------------------------------
                                         Name:  G.D. FAIRSERVICE
                                         Title: DEPUTY CHIEF EXECUTIVE


                                  CANDOVER PARTNERS LIMITED
                                  (as general partner of the
                                  Candover 1994 UK No.2 Limited
                                  Partnership)


                                     by  /s/ G.D. Fairservice
                                         -----------------------------------
                                         Name:  G.D. FAIRSERVICE
                                         Title: DEPUTY CHIEF EXECUTIVE


                                  CANDOVER PARTNERS LIMITED
                                  (as general partner of the
                                  Candover 1994 US No. 1 Limited
                                  Partnership)


                                     by  /s/ G.D. Fairservice
                                         ------------------------------------
                                         Name:  G.D. FAIRSERVICE
                                         Title: DEPUTY CHIEF EXECUTIVE
<PAGE>

                                       CANDOVER PARTNERS LIMITED
                                       (as general partner of the
                                       Candover 1994 US No. 2 Limited
                                       Partnership)


                                           by   /s/ G.D. Fairservice
                                                -----------------------------
                                                Name:  G.D. FAIRSERVICE
                                                Title: DEPUTY CHIEF EXECUTIVE
<PAGE>

                                           TED B. MILLER, JR.

                                              by /s/ Ted B. Miller, Jr.
                                                 ----------------------
                                                  Ted B. Miller, Jr.

<PAGE>

                                       ROBERT A. CROWN


                                          by  /s/Robert A. Crown
                                              -----------------------
                                              Robert A. Crown


                                       BARBARA A. CROWN


                                          by  /s/Barbara A. Crown
                                              -----------------------
                                              Barbara A. Crown


                                       ROBERT A. CROWN AND PNC BANK,
                                       DELAWARE, TRUSTEES OF THE
                                       ROBERT A. CROWN GRANTOR
                                       RETAINED ANNUITY TRUST


                                          by  /s/Robert A. Crown
                                              -----------------------
                                              Name:  Robert A. Crown
                                              Title: Trustee


                                       BARBARA A. CROWN AND PNC BANK,
                                       DELAWARE, TRUSTEES OF THE
                                       BARBARA A. CROWN GRANTOR
                                       RETAINED ANNUITY TRUST


                                          by  /s/Barbara A. Crown
                                              -----------------------
                                              Name:  Barbara A. Crown
                                              Title: Trustee
<PAGE>

                                             BERKSHIRE FUND III
                                             A LIMITED PARTNERSHIP

                                             By: /s/ Carl Ferenbach
                                                 -------------------------------
                                                 a Managing Member

                                             BERKSHIRE FUND IV,
                                             LIMITED PARTNERSHIP

                                             By: /s/ Carl Ferenbach
                                                 -------------------------------
                                                 a Managing Member

                                             BERKSHIRE INVESTORS LLC

                                             By: /s/ Carl Ferenbach
                                                 -------------------------------
                                                 a Managing Member

                                      16
<PAGE>

                                          CENTENNIAL FUND IV, L.P.

                                             by  Centennial Holdings V, L.P.,
                                                 its General Partner


                                                 by  /s/ Jeffrey H. Schutz
                                                     ------------------------
                                                     Name:  Jeffrey H. Schutz
                                                     Title: General Partner


                                                 by
                                                     ------------------------
                                                     Name:
                                                     Title:


                                          CENTENNIAL FUND V, L.P.

                                             by  Centennial Holdings V, L.P.
                                                 its General Partner


                                             by  /s/ Jeffrey H. Schutz
                                                 ----------------------------
                                                 Name:  Jeffrey H. Schutz
                                                 Title: General Partner


                                          CENTENNIAL ENTREPRENEURS FUND V,
                                          L.P.


                                             by  /s/ Jeffrey H. Schutz
                                                 ----------------------------
                                                 Name:  Jeffrey H. Schutz
                                                 Title: General Partner
<PAGE>

                                          NASSAU CAPITAL PARTNERS II, L.P.

                                             by  Nassau Capital L.L.C., its
                                                 General Partner


                                             by  /s/ Randall A. Hack
                                                 -------------------------------
                                                 Name:  Randall A. Hack
                                                 Title: Senior Managing Director
<PAGE>

                                          NAS PARTNERS I, L.L.C.


                                             by  /s/ Randall A. Hack
                                                 -------------------------------
                                                 Name:  Randall A. Hack
                                                 Title: Senior Managing Director
<PAGE>

                                       FAY, RICHWHITE COMMUNICATIONS
                                       LIMITED

                                       by /s/ [ILLEGIBLE]
                                         --------------------------
                                          Name:
                                          Title:
<PAGE>

                                          PNC VENTURE CORP.

                                             by /s/ David McL. Hillman
                                                -----------------------
                                                 Name:  David McL. Hillman
                                                 Title: Exec. V.P.
<PAGE>

                                          AMERICAN HOME ASSURANCE COMPANY


                                             by  /s/ David Pinkerton
                                                 ------------------------
                                                 Name:  David Pinkerton
                                                 Title: Vice President
<PAGE>

                                             NEW YORK LIFE INSURANCE COMPANY


                                               by  /s/ Steven M. Benevento
                                                   --------------------------
                                                   Name:  STEVEN M. BENEVENTO
                                                   Title: Director
<PAGE>

                                     THE NORTHWESTERN MUTUAL LIFE
                                     INSURANCE COMPANY

                                         by /s/ A. Kipp Koester
                                            -------------------------
                                            Name:  A. Kipp Koester
                                            Title: its authorized representative
<PAGE>

                                       HARVARD PRIVATE CAPITAL
                                       HOLDINGS, INC.

                                            by  /s/ Tim R. Palmer
                                               ---------------------
                                               Name:  Tim R. Palmer
                                               Title: Authorized Signatory

<PAGE>


                                              PRIME VIII, L.P.

                                                  by  /s/ Danny Fennewald
                                                     ------------------------
                                                     Name:   DANNY FENNEWALD
                                                     Title:  Treasurer


<PAGE>

                                                                      Exhibit 16

                             AMENDMENT NUMBER TWO
                           TO STOCKHOLDERS AGREEMENT

     AMENDMENT, dated effective as of May 24, 1999, to the Stockholders
Agreement ("the Stockholders Agreement"), dated as of August 21, 1998, among
CROWN CASTLE INTERNATIONAL CORP., a Delaware corporation (the "Company") and
                                                               -------
each of the STOCKHOLDERS of the Company listed in Schedule I thereto
(collectively, the "Stockholders" and each individually, a "Stockholder").
                    ------------                            -----------
     WHEREAS, pursuant to Section 6.04 of the Stockholders Agreement, the
Stockholders Agreement may be amended by the mutual agreement of the parties
thereto;

     WHEREAS, the Company and the Stockholders (including Robert A. Crown and
Barbara A. Crown) have agreed to amend the Stockholders Agreement in the
respects hereinafter set forth;

     NOW, THEREFORE, in consideration of the promises and the respective
agreements hereinafter set forth and set forth in the Stockholders Agreement,
the parties hereto agree as follows;

     SECTION 1. Amendment.  Section 3.10 of the Stockholders Agreement is
                ---------
amended to read as follows:

     "SECTION 3.10.  Company Name. So long as the Ownership Interest of the
                     ------------
     Crown Group is at least 1% or they otherwise consent in writing, the
     Company covenants and agrees (subject to the limitations below) to use its
     best efforts to (i) retain a name beginning with "Crown Castle", (ii)
     retain or cause the name of its principal affiliate owning communication
     towers in the United States to begin with "Crown," (iii) upon a merger,
     consolidation, amalgamation, roll-up or any other transaction with a
     similar effect involving the Company (including, without limitation, a
     merger or roll-up involving Castle Transmission Services (Holdings) Ltd. or
     any of its Affiliates), cause the successor or surviving entity to retain
     or have a name beginning with "Crown Castle," (iv) cause the corporate
     names of all of the Company's subsidiaries conducting significant business
     in the United States to begin with "Crown" other than The TEA Group Inc.,
     TeleStructures Inc. and Spectrum Site Management Corporation and any other
     subsidiary with goodwill associated with the corporate name as determined
     by the Board in its reasonable discretion, and (v) cause Crown Castle and
     all of its subsidiaries worldwide to retain the "CCIC Logo". For purposes
                                                      ---------
     of this Agreement, the "CCIC Logo" shall be a logo in the form attached
     hereto as Exhibit "A" which is incorporated herein by reference.
     Notwithstanding the above, the above covenants and agreement shall not (a)
     require the Company (including any successor entity), any stockholder of
     the Company or member of the Board to incur any costs, expenses or losses
     of any nature or amount including, without limitation, losses relating to
     potential corporate opportunity or foregone stockholder value (price,
     content or any other item), (b) prevent or delay the Company (including any
     successor entity) form consummating or negotiating any

<PAGE>

     proposed transaction or (c) require any member of the Board to breach any
     duty and obligation to the Company or its stockholders. Consent of the
     Crown Group shall be deemed given if written consent is obtained from
     members of the Crown Group holding more than 50% of the Common Stock held
     by such persons at the time of the determination."

     SECTION 2. Construction: Continuing Effect.  This agreement shall be
                -------------------------------
construed in connection with and as part of the Stockholders Agreement and each
reference to the Stockholders Agreement contained in any other document shall
mean the Stockholders Agreement as amended hereby. As amended hereby, the
Stockholders Agreement shall continue in full force and effect.

     SECTION 3. Counterparts.  This Agreement may be executed in one or more
                ------------
counterparts, each of which shall be deemed an original but which together shall
constitute but one instrument. It shall not be necessary for each party to sign
each counterpart so long as every party has signed at least one counterpart.

     IN WITNESS WHEREOF, each party hereto has executed this Agreement as of the
day and year first above written.
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Two to Stockholders Agreement


May 28, 1999                          TELEDIFFUSION DE FRANCE
                                      INTERNATIONAL S.A.

                                      By:  /s/ Michel Azibert
                                           ------------------
                                           Name: Michel Azibert
                                           Title: Chairman

May 28, 1999                          DIGITAL FUTURE INVESTMENTS B.V.

                                      By:  /s/ Michel Azibert
                                           ------------------
                                           Name: Michel Azibert
                                           Title: as Chairman of TeleDiffusion
                                                  de France International S.A.,
                                                  Managing Director

<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Two to Stockholders Agreement


May 27, 1999                            CROWN CASTLE INTERNATIONAL CORP.

                                        By:  /s/ Ted B. Miller, Jr.
                                             ---------------------------
                                             Name: Ted B. Miller, Jr.
                                             Title: Chairman, CEO

<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Two to Stockholders Agreement


May __, 1999                            CANDOVER INVESTMENTS, PLC

                                        By:  /s/ Gavin Douglas Fairservice
                                             -----------------------------
                                             Name: Gavin Douglas Fairservice
                                             Title: Deputy Chairman

May __, 1999                            CANDOVER (TRUSTEES) LIMITED

                                        By:  /s/ Gavin Douglas Fairservice
                                             -----------------------------
                                             Name: Gavin Douglas Fairservice
                                             Title: Deputy Chief Executive

May __, 1999                            CANDOVER PARTNERS LIMITED
                                        (as general partner of the Candover
                                        1994 UK Limited Partnership)

                                        By:  /s/ Gavin Douglas Fairservice
                                             -----------------------------
                                             Name: Gavin Douglas Fairservice
                                             Title: Deputy Chief Executive

May __, 1999                            CANDOVER PARTNERS LIMITED
                                        (as general partner of the Candover
                                        1994 UK No. 2 Limited Partnership)

                                        By:  /s/ Gavin Douglas Fairservice
                                             -----------------------------
                                             Name: Gavin Douglas Fairservice
                                             Title: Deputy Chief Executive

May __, 1999                            CANDOVER PARTNERS LIMITED
                                        (as general partner of the Candover
                                        1994 US No. 1 Limited Partnership)

                                        By:  /s/ Gavin Douglas Fairservice
                                             -----------------------------
                                             Name: Gavin Douglas Fairservice
                                             Title: Deputy Chief Executive

<PAGE>

May __, 1999                            CANDOVER PARTNERS LIMITED
                                        (as general partner of the Candover 1994
                                        US No. 2 Limited Partnership)

                                        By:  /s/ Gavin Douglas Fairservice
                                             -----------------------------
                                             Name: Gavin Douglas Fairservice
                                             Title: Deputy Chief Executive

<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Two to Stockholders Agreement



May __, 1999                            /s/ Ted B. Miller, Jr.
                                        ----------------------------------
                                        TED B. MILLER, JR.


May __, 1999                            /s/ Robert H. Singleton
                                        ----------------------------------
                                        ROBERT H. SINGLETON, Trustee
                                        The Miller 1996 Gift Trusts
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Two to Stockholders Agreement


May __, 1999                            /s/ Robert A. Crown
                                        ----------------------------------
                                        ROBERT A. CROWN


May __, 1999                            /s/ Barbara A. Crown
                                        ----------------------------------
                                        BARBARA A. CROWN


May __, 1999                            RC INVESTORS CORP.
                                        a Delaware corporation

                                        By:  /s/ Robert A. Crown
                                           -------------------------------
                                        Name:  Robert A. Crown
                                             -----------------------------
                                        Title:  President
                                              ----------------------------


May __, 1999                            BC INVESTORS CORP.
                                        a Delaware corporation

                                        By:  /s/ Barbara A. Crown
                                           -------------------------------
                                        Name:  Barbara A. Crown
                                             -----------------------------
                                        Title:  President
                                              ----------------------------
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Two to Stockholders Agreement


May __, 1999                            AMERICAN HOME ASSURANCE COMPANY

                                        By:  /s/ David B. Pinkerton
                                           -------------------------------
                                           Name:  David B. Pinkerton
                                           Title:  Vice President
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Two to Stockholders Agreement


May 28, 1999                  THE NORTHWESTERN MUTUAL LIFE
                              INSURANCE COMPANY

                              By: /s/ A. Kipp Koester
                                  -----------------------------
                                  Name:  A. Kipp Koester
                                  Title: Its authorized representative
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Two to Stockholders Agreement


May __, 1999                           CENTENNIAL FUND IV, L.P.
                                       By:  Centennial Holdings V, L.P.
                                            its general partner


                                       By:  /s/ Jeffrey H. Schutz
                                            -------------------------------
                                            Name:
                                            Title:


May __, 1999                           CENTENNIAL FUND V, L.P.
                                       By:  Centennial Holdings V, L.P.
                                            its general partner


                                       By:  /s/ Jeffrey H. Schutz
                                            -------------------------------
                                            Name:
                                            Title:


May __, 1999                           CENTENNIAL ENTREPRENEURS FUND V, L.P.
                                       By:  Centennial Holdings V, L.P.
                                            its general partner


                                       By:  /s/ Jeffrey H. Schutz
                                            -------------------------------
                                            Name:
                                            Title:


<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Two to Stockholders Agreement


May 27, 1999                           PRIME VIII, L.P.
                                       By:  Prime SKA I, LLC
                                            its general partner


                                       By:  /s/ R. W. Hughes
                                            -------------------------------
                                            Name:
                                            Title:


<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Two to Stockholders Agreement


May 27, 1999                           BERKSHIRE FUND III,
                                       A LIMITED PARTNERSHIP


                                       By:  /s/ Carl Ferenbach
                                            -------------------------------
                                            a Managing Member


May 27, 1999                           BERKSHIRE FUND IV,
                                       LIMITED PARTNERSHIP


                                       By:  /s/ Carl Ferenbach
                                            -------------------------------
                                            a Managing Member


May 27, 1999                           BERKSHIRE INVESTORS LLC


                                       By:  /s/ Carl Ferenbach
                                            -------------------------------
                                            a Managing Member

<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Two to Stockholders Agreement


May 27, 1999                           NASSAU CAPITAL PARTNERS II, L.L.P.

                                       By Nassau Capital L.L.C.
                                       its General Partner


                                       By:  /s/ Randall A. Hack
                                            -------------------------------
                                            Name:  Randall A. Hack
                                            Title: Member



May 27, 1999                           NAS PARTNERS I, L.L.C.


                                       By:  /s/ Randall A. Hack
                                            -------------------------------
                                            Name:  Randall A. Hack
                                            Title: Member

<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Two to Stockholders Agreement


May __, 1999                            FAY, RICHWHITE COMUNICATIONS
                                        LIMITED

                                        By:  /s/ L. R. Davis
                                           -------------------------------
                                           Name:  L. R. Davis
                                           Title:
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Two to Stockholders Agreement


May __, 1999                            FNC VENTURE CORP.

                                        By:  /s/ David McL. Hillman
                                           -------------------------------
                                           Name:  David McL. Hillman
                                           Title:  Executive VP
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Two to Stockholders Agreement


June 10, 1999                           NEW YORK LIFE INSURANCE COMPANY

                                        By:  Ilze Gobins
                                           -------------------------------
                                           Name:  Ilze Gobins
                                           Title:  Investment Manager
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Two to Stockholders Agreement


May __, 1999                            HARVARD PRIVATE CAPITAL
                                        HOLDINGS, INC.

                                        By:  /s/ Michael R. Eisenson
                                           -------------------------------
                                           Name:  Michael R. Eisenson
                                           Title:  Authorized Signatory

<PAGE>

                                                                     EXHIBIT 17

                            AMENDMENT NUMBER THREE
                           TO STOCKHOLDERS AGREEMENT


    AMENDMENT, dated as of August 11, 1999, to the Stockholders Agreement (the
"Stockholders Agreement") dated as of August 21, 1998, as previously amended by
amendments number one and two, among CROWN CASTLE INTERNATIONAL CORP., a
Delaware corporation (the "Company") and each of the STOCKHOLDERS of the Company
listed on Schedule I thereto (collectively, the "Stockholders" and each
individually, a "Stockholder");

     WHEREAS, Robert A. Crown, Barbara A. Crown, RC Investors Corp., BC
Investors Corp., the Grantor Retained Annuity Trust of Robert A. Crown, the
Grantor Retained Annuity Trust of Barbara A. Crown, RACG Holdings LLC, BACG
Holdings LLC and Crown Management Services (collectively, the "Crown Group") and
the Company have entered into an agreement dated August 5, 1999 (the "Crown
Agreement") with respect to certain separation arrangements involving the Crown
Group;

    WHEREAS, the Company and the Crown Group have proposed to enter into certain
transactions (the "DECS Transactions") involving the issuance and sale by DECS
Trust V, a Delaware business trust (the "DECS Trust"), of a minimum of 5,000,000
and a maximum of 5,645,000 DECS securities as set forth in greater detail in the
registration statement on Form N-2 (Registration No. 333-83965) filed by the
DECS Trust with the Securities and Exchange Commission and in an Underwriting
Agreement among the DECS Trust, the Company, the Crown Group, Salomon Smith
Barney Inc. and Goldman, Sachs & Co. and four Forward Purchase Agreements among
RC Investors, BC Investors, BACG and RACG, respectively, and the DECS Trust;

    WHEREAS, the Crown Group entered into the Crown Agreement in part as
consideration for participation by the Company in the consummation of the DECS
Transactions;

    WHEREAS, pursuant to Section 6.04 of the Stockholders Agreement, the
Stockholders Agreement may be amended by the mutual agreement of the parties
thereto;

    WHEREAS, the Company and the Stockholders (including Robert A. Crown and
Barbara A. Crown) have agreed to amend the Stockholders Agreement in the manner
hereinafter set forth;

    NOW, THEREFORE, in consideration of the promises and the respective
agreements, acknowledgments and confirmations hereinafter set forth and set
forth in the Stockholders Agreement, the parties hereto agree as follows;

    SECTION 1. Amendment. (a) The Company and the Stockholders hereby agree that
               ----------
all rights, responsibilities or other obligations of any kind or nature
whatsoever relating to the Crown Group and arising under the Stockholders
Agreement other than the rights of the Crown
<PAGE>

Group as set forth in Section 3.10 of the Stockholders Agreement shall hereby be
terminated, including, without limitation, the Crown Group's existing obligation
(as set forth in Section 3.05 of the Stockholders Agreement) to vote or act by
written consent in favor of, or against, the election of any persons nominated
to be a Director of the Company.

    (b)  Section 3.10 of the Stockholders Agreement is amended to read as
    follows:

    "SECTION 3.10.  Company Name.  So long as the Ownership Interest of the
                    ------------
    Crown Group is at least 1% or they otherwise consent in writing, the Company
    covenants and agrees (subject to the limitations below) to use its best
    efforts to (i) retain a name beginning with "Crown Castle", (ii) retain or
    cause the name of its principal affiliate owning communication towers in the
    United States to begin with "Crown," (iii) upon a merger, consolidation,
    amalgamation, roll-up or any other transaction with a similar effect
    involving the Company (including, without limitation, a merger or roll-up
    involving Castle Transmission Services (Holdings) Ltd. or any of its
    Affiliates), cause the successor or surviving entity to retain or have a
    name beginning with "Crown Castle," (iv) cause the corporate names of all of
    the Company's subsidiaries conducting significant business in the United
    States to begin with "Crown" other than The TEA Group Inc., TeleStructures
    Inc. and Spectrum Site Management Corporation and any other subsidiary with
    goodwill associated with the corporate name as determined by the Board in
    its reasonable discretion, and (v) cause Crown Castle and all of its
    subsidiaries worldwide to retain the "CCIC Logo". For purposes of this
                                          ---------
    Agreement, the "CCIC Logo" shall be a logo in the form attached hereto as
    Exhibit "A" which is incorporated herein by reference. Notwithstanding the
    above, the above covenants and agreement shall not (a) require the Company
    (including any successor entity), any stockholder of the Company or member
    of the Board to incur any costs, expenses or losses of any nature or amount
    including, without limitation, losses relating to potential corporate
    opportunity or foregone stockholder value (price, content or any other
    item), (b) prevent or delay the Company (including any successor entity)
    from consummating or negotiating any proposed transaction or (c) require any
    member of the Board to breach any duty and obligation to the Company or its
    stockholders. Consent of the Crown Group shall be deemed given if written
    consent is obtained from members of the Crown Group holding more than 50% of
    the Common Stock held by such persons at the time of the determination."

    SECTION 2. Acknowledgements. The Company and each Stockholder acknowledges
               ----------------
and confirms the following:

         (a)  For purposes solely of Section 3.10 of the Stockholders Agreement,
              the Crown Group shall be deemed to retain their Ownership Interest
              in the Shares subject to the DECS Transactions (the "DECS
              Shares"), so long as either (i) the Crown Group retains beneficial
              ownership of the DECS Shares or (ii) the DECS Shares continue to
              be held by a custodian pursuant to the terms of the Forward
              Purchase Agreements.






<PAGE>

         (b)  In connection with the DECS Transactions, the Crown Group has
              complied in all respects with its obligations under the provisions
              of Article II of the Stockholders Agreement.

         (c)  Any tag-along or transfer rights or other restrictions (as set
              forth in Article V of the Stockholders Agreement) with respect to
              any present or future sale of the Shares in connection with the
              Crown Group's DECS Transactions and any right to register Company
              securities (as set forth in Article IV of the Stockholders
              Agreement) by means of the DECS Registration Statement filed as
              part of the Crown Group's DECS Transactions have been waived by
              such Stockholder.

     SECTION 3.  Construction; Continuing Effect.  This Agreement shall be
                 --------------------------------
construed in connection with and as part of the Stockholders Agreement and each
reference to the Stockholders Agreement contained in any other document shall
mean the Stockholders Agreement as amended hereby. As amended hereby, the
Stockholders Agreement shall continue in full force and effect. Terms used but
not defined in this Amendment Number Three to Stockholders Agreement shall have
the meaning ascribed to such term in the Stockholders Agreement.

     SECTION 4.  Counterparts.  This Agreement may be executed in one or more
                 -------------
counterparts, each of which shall be deemed an original but which together shall
constitute but one instrument. It shall not be necessary for each party to sign
each counterpart so long as every party has signed at least one counterpart.

     IN WITNESS WHEREOF, each party hereto has executed this Agreement as of the
day and year first above written.

<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Three to Stockholders Agreement



August 11, 1999                        CROWN CASTLE INTERNATIONAL CORP.

                                        By: /s/ Kathy Broussard
                                           --------------------
                                        Name: Kathy Broussard
                                        Title: Vice President
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Three to Stockholders Agreement


August 16, 1999                        TELEDIFFUSION DE FRANCE
                                       INTERNATIONAL S.A.

                                       By: /s/ Michel Azibert
                                          -------------------
                                       Name: Michel Azibert
                                       Title: Chairman

August 16, 1999                        DIGITAL FUTURE INVESTMENTS B.V.

                                       By: /s/ Michel Azibert
                                           ------------------
                                       Name: Michel Azibert
                                       Title: Managing Director

<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Three to Stockholders Agreement


August __, 1999                        CANDOVER INVESTMENTS, PLC

                                       By: /s/ G. D. Fairservice
                                           -------------------------------
                                       Name:
                                       Title:

August __, 1999                        CANDOVER (TRUSTEES) LIMITED

                                       By: /s/ G. D. Fairservice
                                           -------------------------------
                                       Name:
                                       Title:

August __, 1999                        CANDOVER PARTNERS LIMITED
                                       (as general partner of the Candover 1994
                                       UK Limited Partnership)

                                       By: /s/ G. D. Fairservice
                                           -------------------------------
                                       Name:
                                       Title:

August __, 1999                        CANDOVER PARTNERS LIMITED
                                       (as general partner of the Candover 1994
                                       UK No. 2 Limited Partnership)

                                       By: /s/ G. D. Fairservice
                                           -------------------------------
                                       Name:
                                       Title:

August __, 1999                        CANDOVER PARTNERS LIMITED
                                       (as general partner of the Candover 1994
                                       U.S. No. 1 Limited Partnership)

                                       By: /s/ G. D. Fairservice
                                           -------------------------------
                                       Name:
                                       Title:
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Three to Stockholders Agreement


August __, 1999                        CANDOVER PARTNERS LIMITED
                                       (as general partner of the Candover 1994
                                       U.S. No. 2 Limited Partnership)

                                       By: /s/ G. D. Fairservice
                                           ------------------------------------
                                       Name:
                                       Title
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Three to Stockholders Agreement



August 11, 1999                           /s/ Ted B. Miller, Jr.
                                          -------------------------------
                                          TED B. MILLER, JR.


August 11, 1999
                                          -------------------------------
                                          ROBERT H. SINGLETON, Trustee
                                          The Miller 1996 Gift Trusts
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Three to Stockholders Agreement



August ___, 1999                       By:
                                          -------------------------------
                                          TED B. MILLER, JR.


August 12, 1999                        By:/s/ Robert H. Singleton
                                          -------------------------------
                                          ROBERT H. SINGLETON, Trustee
                                          The Miller 1996 Gift Trusts
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Three to Stockholders Agreement



August 11, 1999                        /s/ Robert A. Crown
                                       -----------------------------------
                                       ROBERT A. CROWN


August 11, 1999                        /s/ Barbara A. Crown
                                       -----------------------------------
                                       BARBARA A. CROWN


August 11, 1999                        RC INVESTORS CORP.
                                       a Delaware corporation

                                       By:/s/ Robert A. Crown
                                          --------------------------------
                                       Name:
                                       Title:


August 11, 1999                        BC INVESTORS CORP.
                                       a Delaware corporation

                                       By:/s/ Barbara A. Crown
                                          --------------------------------
                                       Name:
                                       Title:


August 11, 1999                        RACG Holdings LLC
                                       Limited Liability Company

                                       By:/s/ Robert A. Crown
                                          --------------------------------
                                       Name:
                                       Title:


August 11, 1999                        BACG Holdings LLC
                                       Limited Liability Company

                                       By:/s/ Barbara A. Crown
                                          --------------------------------
                                       Name:
                                       Title:

<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Three to Stockholders Agreement


August 12, 1999                        BERKSHIRE FUND III
                                       A LIMITED PARTNERSHIP

                                       By: /s/ Carl Ferenbach
                                          ---------------------------
                                          a Managing Member


August 12, 1999                        BERKSHIRE FUND IV
                                       LIMITED PARTNERSHIP

                                       By: /s/ Carl Ferenbach
                                          ---------------------------
                                          a Managing Member


August 12, 1999                        BERKSHIRE INVESTORS LLC

                                       By: /s/ Carl Ferenbach
                                          ---------------------------
                                          a Managing Member
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Three to Stockholders Agreement


August 11, 1999                        NASSAU CAPITAL PARTNERS II, L.P.

                                       By Nassau Capital L.L.C.,
                                       its General Partner

                                       By: /s/ John G. Quigley
                                           ------------------------------
                                           Name:  John G. Quigley
                                           Title: Member


August 11, 1999                        NAS PARTNERS I, L.L.C.

                                       By: /s/ John G. Quigley
                                           ------------------------------
                                           Name:  John G. Quigley
                                           Title: Member
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Three to Stockholders Agreement


August 12, 1999                        FAY, RICHWHITE COMMUNICATIONS
                                       LIMITED

                                       By: /s/ Leigh Davis
                                           -------------------------------
                                       Name: LEIGH DAVIS
                                       Title: Director
                                              FRC #2
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Three to Stockholders Agreement


August 11, 1999                        PNC VENTURE CORP.

                                       By: /s/ Gary Bentnor
                                          ---------------------------
                                          Name:
                                          Title: Pres.
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Three to Stockholders Agreement


August 11, 1999                        NEW YORK LIFE INSURANCE COMPANY

                                       By:  /s/  Steven M. Benevento
                                          ----------------------------
                                          Name:   Steven M. Benevento
                                          Title:  Director

<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Three to Stockholders Agreement


August 11, 1999                        HARVARD PRIVATE CAPITAL
                                       HOLDINGS, INC.

                                       By:  /s/  Michael Thonis
                                          ---------------------------
                                       Name:  Michael Thonis
                                       Title: Authorized Signatory

<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Three to Stockholders Agreement



August 11, 1999                        AMERICAN HOME ASSURANCE COMPANY

                                       By: /s/  David Pinkerton
                                           ----------------------------
                                           Name:  David Pinkerton
                                           Title: Vice President
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Three to Stockholders Agreement


August 13, 1999                        THE NORTHWESTERN MUTUAL LIFE
                                       INSURANCE COMPANY

                                       By: /s/ Richard A. Strait
                                           ------------------------------
                                       Name: Richard A. Strait
                                       Title: Its authorized representative

<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Three to Stockholders Agreement


August 11, 1999                        CENTENNIAL FUND IV, L.P.
                                       By:  Centennial Holdings IV, L.P.
                                            its general partner

                                       By:  /s/ Jeffrey H. Schutz
                                          -------------------------------------
                                          Name:
                                          Title:


August 11, 1999                        CENTENNIAL FUND V, L.P.
                                       By:  Centennial Holdings V, L.P.
                                            its general partner

                                       By:  /s/ Jeffrey H. Schutz
                                          -------------------------------------
                                          Name:
                                          Title:


August 11, 1999                        CENTENNIAL ENTREPRENEURS FUND V, L.P.
                                       By:  Centennial Holdings V, L.P.
                                            its general partner

                                       By:  /s/ Jeffrey H. Schutz
                                          -------------------------------------
                                          Name:
                                          Title:
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Three to Stockholders Agreement


August 11, 1999                        PRIME VIII, L.P.
                                       By:  Prime SKA I, LLC
                                            its general partner

                                       By:  /s/  Duncan J. Butler, Jr.
                                          ---------------------------
                                          Name:  Duncan J. Butler, Jr.
                                          Title: Member

<PAGE>

                                                                      Exhibit 18

                             AMENDMENT NUMBER FOUR
                           TO STOCKHOLDERS AGREEMENT

        AMENDMENT, dated effective October 1, 1999, to the Stockholders
Agreement (the "Stockholders Agreement") dated as of August 21, 1998, among
CROWN CASTLE INTERNATIONAL CORP., a Delaware corporation (the "Company") and
each of the STOCKHOLDERS of the Company listed on Schedule I thereto
(collectively, the "Stockholders" and each individually, a "Stockholder");

        WHEREAS, the Company and the Stockholders desire to amend the
Stockholders Agreement to provide that Shares distributed by a Stockholder to a
partner, member, stockholder or beneficiary of such Stockholder shall cease to
be a subject to the Stockholders Agreement and the distribution of such Shares
shall not cause the distributee to be a Stockholder;

        WHEREAS, pursuant to Section 6.04 of the Stockholders Agreement, the
Stockholders Agreement may be amended by the mutual agreement of the parties
thereto;
and

        WHEREAS, the Company and the Stockholders have agreed to amend the
Stockholders Agreement in the manner hereinafter set forth.

        NOW, THEREFORE, in consideration of the promises and the respective
agreements, acknowledgments and confirmations hereinafter set forth and set
forth in the Stockholders Agreement, the parties hereto agree as follows:

        SECTION 1.  Amendment
                    ---------
        (a) Section 2.05 of the Agreement is amended and restated to read as
follows:

                "SECTION 2.05. Certain Transferees to Execute Agreement. Each
                               ----------------------------------------
                Stockholder agrees that it will not, directly or indirectly,
                sell or otherwise transfer any Shares held by such Stockholder
                to any of its Affiliates or permitted transferees, unless, prior
                to the consummation of any such sale or transfer, the Affiliate
                or permitted transferee to whom such sale or transfer is
                proposed to be made (a "Prospective Transferee") (i) executes
                and delivers to the Company and each other party to this
                Agreement a counterpart hereof and (ii) represents and warrants
                in writing to the Company that such counterpart has been duly
                authorized, executed and delivered by such Prospective
                Transferee and is a legal, valid and binding obligation of such
                Prospective Transferee enforceable against it in accordance with
                its terms, subject to insolvency, bankruptcy and other laws
                affecting creditors generally. Upon the execution and delivery
                by such Prospective Transferee of the documents referred to in
                the preceding sentence, such Prospective Transferee shall be
                deemed a "Stockholder" for the purposes of this Agreement, and
                shall have the rights and be subject to the obligations of a
                Stockholder hereunder with respect to the Shares held by such
                Prospective Transferee. The provisions of this Section 2.05
                shall not apply to any distribution of Shares by a Stockholder
                to its partners (in the case of a partnership), members (in the
                case of a limited liability company), stockholders (in the case
                of a corporation) or beneficiaries (in the case of a trust) of
                such Stockholder whether or not the distributee is a
                Stockholder, Affiliate or permitted transferee."

                (b) Section 2.06 of the Agreement is amended and restated to
read as follows:

                        "SECTION 2.06. Sale to a Third Party; Distributions. If
                                       ------------------------------------
                a sale or transfer of Shares is made by a Stockholder to a third
                party (except for transfers within the TDF Group, the Berkshire
                Group, the Centennial Group, the Candover Group, the Nassau
                Group or otherwise to an Affiliate or to any permitted
                transferee) (a "Third Party Transferee"), such Shares shall
                immediately cease to be subject to this Agreement and such Third
                Party Transferee will not become a Stockholder for purposes of
                this Agreement. If a sale or transfer of Shares results in the
                selling Stockholder or a permitted transferee ceasing to own any
                Shares, such selling Stockholder shall cease to be a Stockholder
                for purposes of this Agreement. If a Stockholder distributes
                Shares to any of its partners (in the case of a partnership),
                members (in the case of a limited liability company),
                stockholders (in the case of a corporation) or beneficiaries (in
                the case of a trust), such Shares shall immediately cease to be
                subject to this Agreement (whether or not the distributee is a
                Stockholder, a member of the TDF Group, the Berkshire Group, the
                Centennial Group, the Candover Group, the Nassau Group, an
                Affiliate or a permitted transferee) and such partner, member,
                stockholder or beneficiary will not become a Stockholder for
                purposes of this Agreement as a result of such distribution."

                        SECTION 3. Construction Continuing Effect. This
                                   ------------------------------
                Agreement shall be construed in connection with and as part of
                the Stockholders Agreement and each reference to the
                Stockholders Agreement contained in any other document shall
                mean the Stockholders Agreement as amended hereby. As amended
                hereby, the Stockholders Agreement shall continue in full force
                and effect. Terms used but not defined in this Amendment Number
                Four to Stockholders Agreement shall the meaning ascribed to
                such term in the Stockholders Agreement.

                        SECTION 4. Counterparts. This Agreement may be executed
                                   ------------
                in one or more counterparts, each of which shall be deemed an
                original but which together shall constitute but one instrument.
                It shall not be necessary for each party to sign each
                counterpart so long as every party has signed at least one
                counterpart.

                        IN WITNESS WHEREOF, each party hereto has executed this
                Agreement effective as of the day and year first above written.

<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Four to Stockholders Agreement






August __,1999                          CROWN CASTLE INTERNATIONAL CORP.


                                        By: /s/ Ted B. Miller, Jr.
                                           _____________________________
                                           Name: Ted B. Miller, Jr.
                                           Title: CEO
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Four to Stockholders Agreement



August __, 1999                     TELEDIFFUSION DE FRANCE
                                    INTERNATIONAL S.A.


                                    By: /s/ Michel Azibert
                                       _____________________________
                                       Name:  Michel Azibert
                                       Title: Chairman

August __, 1999                     DIGITAL FUTURE INVESTMENTS D.V.


                                    BY:  /s/ Michel Azibert
                                       _____________________________
                                       Name: Michel Azibert
                                       Title: Managing Director



<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Four to Stockholders Agreement



August __, 1999                     CANDOVER INVESTMENTS, PLC.


                                    By:  /s/ G. D. Fairservice
                                       ______________________________
                                       Name:
                                       Title:

August   , 1999                     CANDOVER (TRUSTEES) LIMITED
       __

                                    By:  /s/ G. D. Fairservice
                                       ______________________________
                                       Name:
                                       Title:

August __, 1999                     CANDOVER PARTNERS LIMITED
                                    (as general partner of the Candover 1994
                                    UK Limited Partnership)


                                    By:  /s/ G. D. Fairservice
                                       ______________________________
                                       Name:
                                       Title:

August __, 1999                     CANDOVER PARTNERS LIMITED
                                    (as general partner of the Candover 1994
                                    U.K. No.2 Limited Partnership)


                                    By:  /s/ G. D. Fairservice
                                       ______________________________
                                       Name:
                                       Title:

<PAGE>

August __, 1999                      CANDOVER PARTNERS LIMITED
                                     (as general partner of the Candover 1994
                                     US No. 1 Limited Partnership)


                                     By:   /s/ G. D. Fairservice
                                         _____________________________
                                         Name:
                                         Title:
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Four to Stockholders Agreement
August __, 1999



                                      CANDOVER PARTNERS LIMITED
                                      (as general partner of the Candover 1994
                                      U.S. No. 2 Limited Partnership)


                                      By: /s/ G.D. Fairservice
                                          _________________________________
                                          Name:
                                          Title:

<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Four to Stockholders Agreement




August __, 1999                                  /s/ Ted B. Miller, Jr.
                                                 ______________________________
                                                 TED B. MILLER, JR.


August __, 1999
                                                 ______________________________
                                                 ROBERT H. SINGLETON, Trustee
                                                 The Miller 1996 Gift Trusts
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Four to Stockholders Agreement



August __, 1999
                                                ________________________________
                                                TED B. MILLER JR.


August __, 1999                                 Robert H. Singleton
                                                ________________________________
                                                ROBERT H. SINGLETON JR., Trustee
                                                The Miller 1996 Gift Trusts
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Four to Stockholders Agreement



August __, 1999                                FAY, RICHWHITE COMMUNICATIONS
                                               LIMITED


                                               By: /s/ Leigh Davis
                                                  ____________________________
                                                  Name:  Leigh Davis
                                                  Title: Principal
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Four to Stockholders Agreement


October 13, 1999                            BERKSHIRE FUND III
                                            LIMITED PARTNERSHIP

                                            By: /s/ Carl Ferenbach
                                               _________________________________
                                               a Managing Member


October 13, 1999                            BERKSHIRE FUND IV
                                            LIMITED PARTNERSHIP

                                            By: /s/ Carl Ferenbach
                                               _________________________________
                                               a Managing Member


October 13, 1999                            BERKSHIRE INVESTORS LLC

                                            By: /s/ Carl Ferenbach
                                               _________________________________
                                               a Managing Member

<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Four to Stockholders Agreement


August __, 1999                                 /s/ Robert A. Crown
                                                ______________________________
                                                ROBERT A. CROWN


August __, 1999
                                                /s/ Barbara A. Crown
                                                _______________________________
                                                BARBARA A. CROWN


August __, 1999
                                                RC INVESTORS CORP.
                                                a Delaware corporation

                                                By: /s/ Robert A. Crown
                                                   ____________________________

                                                Name:
                                                     __________________________

                                                Title:
                                                      _________________________


August __, 1999                                 BC INVESTORS CORP.
                                                a Delaware corporation

                                                By: /s/ Barbara A. Crown
                                                   ____________________________

                                                Name:
                                                     __________________________

                                                Title:
                                                      _________________________

August __, 1999                                 RACG Holdings LLC

                                                By: /s/ Robert A. Crown
                                                   ____________________________

                                                Name:
                                                     __________________________

                                                Title:
                                                      _________________________

August __, 1999                                 BACG Holding LLC

                                                By: /s/ Barbara A. Crown
                                                   ____________________________

                                                Name:
                                                     __________________________

                                                Title:
                                                      _________________________

<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Four to Stockholders Agreement


October 14, 1999                              NASSAU CAPITAL PARTNERS II, L.P.

                                              By Nassau Capital L.L.C
                                              its General Partner

                                              By: /s/ Randall A. Hack
                                                 ______________________________

                                                 Name: Randall A. Hack
                                                 Title: Member


October 14, 1999                              NAS PARTNERS I, L.L.C.

                                              By: /s/ Randall A. Hack
                                                 ______________________________

                                                 Name: Randall A. Hack
                                                 Title: Member
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Four to Stockholders Agreement


August __, 1999                                  PNC VENTURE CORP.

                                                 By: /s/ David McL. Hillman
                                                    ____________________________
                                                    Name: David McL. Hillman
                                                    Title: Exec. V. P.
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Four to Stockholders Agreement


August __, 1999                               NEW YORK LIFE INSURANCE COMPANY

                                              By: /s/ Steven M. Benevento
                                                 _______________________________
                                                 Name: STEVEN M. BENEVENTO
                                                 Title: Director
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Four to Stockholders Agreement


August __, 1999                             HARVARD PRIVATE CAPITAL
                                            HOLDINGS, INC.

                                            By: /s/ Mark A. Rosen
                                               ______________________________
                                               Name: Mark A. Rosen
                                               Title: Authorized Signatory
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Four to Stockholders Agreement


August __, 1999                              AMERICAN HOME ASSURANCE COMPANY

                                             By: /s/ David B. Pinkerton
                                                ________________________________
                                                Name: David B. Pinkerton
                                                Title: Vice President
<PAGE>

CROWN CASTLE INTERNATIONAL CORP.
Amendment Number Four to Stockholders Agreement


October 15, 1999                        THE NORTHWESTERN MUTUAL LIFE
                                        INSURANCE COMPANY

                                        By: /s/ A. Kipp Koester
                                           _______________________________
                                           Name: A. Kipp Koester
                                           Title: Its Authorized Representative


<PAGE>

                                                                      Exhibit 19
                                                                      ----------

                            Joint Filing Agreement
                            ----------------------

          In accordance with Rule 13d-1(k) under the Securities Exchange Act of
1934, as amended, the undersigned hereby (i) agree to the joint filing with all
other Candover Reporting Persons (as such term is defined in the amendment to
the statement on Schedule 13D described below) on behalf of each of them of an
amendment to a statement on Schedule 13D with respect to the common stock, par
value $.01 per share, of Crown Castle International Corp. and (ii) agree that
this Agreement be included as an Exhibit to such joint filing.  This Agreement
may be executed in any number of counterparts all of which taken together shall
constitute one and the same instrument.

          IN WITNESS WHEREOF, the undersigned, being duly authorized, hereby
executes this Agreement this 3rd day of November, 1999.

                                  CANDOVER INVESTMENTS PLC

                                  By:  /s/ P. R. Neal
                                       ------------------------------
                                       Name:  P. R. Neal
                                       Title: Company Secretary

                                  CANDOVER (TRUSTEES) LIMITED

                                  By:  /s/ P. R. Neal
                                       ------------------------------
                                       Name:  P. R. Neal
                                       Title: Company Secretary

                                  CANDOVER PARTNERS LIMITED
                                  (as general partner of the Candover 1994 UK
                                  Limited Partnership, the Candover 1994 UK No.2
                                  Limited Partnership, the Candover 1994 US No.1
                                  Limited Partnership and the Candover 1994 US
                                  No.2 Limited Partnership)

                                  By:  /s/ P. R. Neal
                                       ------------------------------
                                       Name:  P. R. Neal
                                       Title: Company Secretary

                                  CANDOVER SERVICES LIMITED

                                  By:  /s/ P. R. Neal
                                       ------------------------------
                                       Name:  P. R. Neal
                                       Title: Company Secretary



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