AMERICAN TOWER CORP /MA/
10-Q, 1999-11-15
COMMUNICATIONS SERVICES, NEC
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                                 UNITED STATES
                      SECURITIES AND EXCHANGE COMMISSION
                            Washington, D.C. 20549

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

                                   FORM 10-Q

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

(Mark One):
[X]Quarterly report pursuant to Section 13 or 15(d) of the Securities Exchange
   Act of 1934. For the quarterly period ended September 30, 1999.

[_]Transition report pursuant to Section 13 or 15(d) of the Securities
Exchange Act of 1934.

                       Commission File Number: 001-14195

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

                          AMERICAN TOWER CORPORATION
            (Exact name of registrant as specified in its charter)

               Delaware                              65-0723837
    (State or other jurisdiction of     (I.R.S. Employer Identification No.)
    incorporation or organization)

               116 Huntington Avenue Boston, Massachusetts 02116
                   (Address of principal executive offices)

                        Telephone Number (617) 375-7500
             (Registrant's telephone number, including area code)

  Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to
such filing requirements for the past 90 days: Yes  X    No ______
                                                    -
<TABLE>
<CAPTION>
                                                                Outstanding at
Class of Common Stock                                         November 1,  1999
- ---------------------                                         ------------------
<S>                                                           <C>
Class A Common Stock......................................... 144,500,686 shares
Class B Common Stock.........................................   8,778,644 shares
Class C Common Stock.........................................   2,422,804 shares
                                                              ------------------
Total........................................................ 155,702,134 shares
                                                              ==================
</TABLE>

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<PAGE>

                           AMERICAN TOWER CORPORATION

                                     INDEX

                                                                        Page No.
                                                                        --------

                         PART I. FINANCIAL INFORMATION

Item 1. Unaudited Condensed Consolidated Financial Statements

<TABLE>
<S>                                                                         <C>
  Condensed Consolidated Balance Sheets
   September 30, 1999 and December 31, 1998................................   3
  Condensed Consolidated Statements of Operations
   Three and Nine Months Ended September 30, 1999 and 1998.................   4
  Condensed Consolidated Statements of Cash Flows
   Nine Months Ended September 30, 1999 and 1998...........................   5
  Notes to Condensed Consolidated Financial Statements.....................   6

Item 2. Management's Discussion and Analysis of Financial Condition and
 Results of Operations.....................................................  13

Item 3. Quantitative and Qualitative Disclosures About Market Risk.........  23
</TABLE>

                           PART II. OTHER INFORMATION

<TABLE>
 <C>     <S>                                                                 <C>
 Item 1. Legal Proceedings.................................................   24
 Item 2. Changes in Securities and Use of Proceeds.........................   24
 Item 6. Exhibits and Reports on Form 8-K..................................   24
         Signatures........................................................   26
</TABLE>

                                       2
<PAGE>

                         PART I. FINANCIAL INFORMATION

ITEM 1. UNAUDITED CONDENSED CONSOLIDATED FINANCIAL STATEMENTS

                  AMERICAN TOWER CORPORATION AND SUBSIDIARIES

                CONDENSED CONSOLIDATED BALANCE SHEETS--UNAUDITED
                       (In thousands, except share data)

<TABLE>
<CAPTION>
                                                     September 30, December 31,
                                                         1999          1998
                                                     ------------- ------------
<S>                                                  <C>           <C>
ASSETS
CURRENT ASSETS:
 Cash and cash equivalents..........................  $   41,711    $  186,175
 Accounts receivable, net of allowance for doubtful
  accounts of $2,308 and $1,230, respectively.......      38,818        15,506
 Prepaid and other current assets...................       9,397         4,065
 Inventories........................................       7,123
 Costs in excess of billings on uncompleted
  contracts.........................................       9,402         1,344
 Deferred income taxes..............................         495           495
 Due from CBS Corporation...........................      12,593
                                                      ----------    ----------
   Total current assets.............................     119,539       207,585
                                                      ----------    ----------
PROPERTY AND EQUIPMENT, net.........................     892,245       449,476
GOODWILL AND OTHER INTANGIBLE ASSETS, net...........   1,275,807       718,575
NOTES RECEIVABLE....................................      72,156         7,585
DEPOSITS AND OTHER LONG-TERM ASSETS.................     133,113         9,406
INVESTMENTS.........................................      14,695           298
DEFERRED INCOME TAXES...............................     113,003       109,418
                                                      ----------    ----------
TOTAL...............................................  $2,620,558    $1,502,343
                                                      ==========    ==========
LIABILITIES AND STOCKHOLDERS' EQUITY
CURRENT LIABILITIES:
 Current portion of long-term debt..................  $    2,653    $    1,652
 Accounts payable...................................      15,497         6,696
 Accrued expenses...................................      24,015        11,347
 Accrued tower construction costs...................      20,142        16,099
 Accrued interest...................................       3,653         1,132
 Billings in excess of costs on uncompleted
  contracts.........................................      11,246         6,610
 Accrued separation expenses........................                     5,058
 Due to CBS Corporation.............................                    45,127
 Accrued acquisition purchase price.................         353        21,914
                                                      ----------    ----------
   Total current liabilities........................      77,559       115,635
                                                      ----------    ----------
LONG-TERM DEBT......................................     375,987       279,477
OTHER LONG-TERM LIABILITIES.........................       3,369         1,429
                                                      ----------    ----------
   Total liabilities................................     456,915       396,541
                                                      ----------    ----------
MINORITY INTEREST IN SUBSIDIARIES...................       5,909         4,116
                                                      ----------    ----------
COMMITMENTS AND CONTINGENCIES
REDEEMABLE CLASS A COMMON STOCK:
   $.01 par value, 336,250 shares issued and
    outstanding; at estimated redemption value of
    $29.56 per share................................                     9,940
                                                      ----------    ----------
STOCKHOLDERS' EQUITY:
 Preferred Stock; $0.01 par value; 20,000,000
  shares authorized; no shares issued or
  outstanding.......................................
 Class A Common Stock; $.01 par value; 500,000,000
  shares authorized; 144,466,550 and 96,291,111
  shares issued and outstanding, respectively.......       1,445           963
 Class B Common Stock, $.01 par value; 50,000,000
  shares authorized; 8,811,940 and 9,001,060 shares
  issued and outstanding, respectively..............          88            90
 Class C Common Stock, $.01 par value; 10,000,000
  shares authorized; 2,422,804 and 3,002,008 shares
  issued and outstanding, respectively..............          24            30
 Additional paid-in capital.........................   2,239,881     1,140,365
 Accumulated deficit................................     (82,176)      (49,702)
                                                      ----------    ----------
   Total............................................   2,159,262     1,091,746
   Less: Treasury stock (76,403 shares at cost).....      (1,528)
                                                      ----------    ----------
   Total stockholders' equity.......................   2,157,734     1,091,746
                                                      ----------    ----------
TOTAL...............................................  $2,620,558    $1,502,343
                                                      ==========    ==========
</TABLE>

           See notes to condensed consolidated financial statements.

                                       3
<PAGE>

                  AMERICAN TOWER CORPORATION AND SUBSIDIARIES

          CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS--(UNAUDITED)
                     (In thousands, except per share data)

<TABLE>
<CAPTION>
                                        Three Months           Nine Months
                                     Ended September 30,   Ended September 30,
                                     --------------------  --------------------
                                       1999       1998       1999       1998
                                     ---------  ---------  ---------  ---------
<S>                                  <C>        <C>        <C>        <C>
REVENUES:

 Rental and management.............  $  37,768  $  17,719  $  94,640  $  39,305
 Services..........................     22,710      6,572     54,948     18,848
 Video, voice, data and Internet
  transmission.....................      7,061      6,187     19,512     13,332
                                     ---------  ---------  ---------  ---------
   Total revenues..................     67,539     30,478    169,100     71,485
                                     ---------  ---------  ---------  ---------

OPERATING EXPENSES:
 Operating expenses excluding
  depreciation and amortization,
  tower separation and corporate
  general and administrative
  expenses:
   Rental and management...........     17,917      8,087     43,488     18,417
   Services........................     17,110      4,677     41,795     15,412
   Video, voice, data and Internet
    transmission...................      5,478      3,928     14,242      8,697
 Depreciation and amortization.....     35,111     17,243     92,919     32,998
 Tower separation expense..........                   159                12,616
 Corporate general and
  administrative expense...........      2,255      1,561      6,395      3,186
                                     ---------  ---------  ---------  ---------
   Total operating expenses........     77,871     35,655    198,839     91,326
                                     ---------  ---------  ---------  ---------
LOSS FROM OPERATIONS...............    (10,332)    (5,177)   (29,739)   (19,841)
                                     ---------  ---------  ---------  ---------

OTHER INCOME (EXPENSE):
 Interest expense..................     (5,958)    (7,121)   (17,497)   (17,023)
 Interest income and other, net....      3,162      4,451     13,899      6,283
 Minority interest in net
  (earnings) losses of
  subsidiaries.....................       (158)       (66)       (79)      (255)
                                     ---------  ---------  ---------  ---------
TOTAL OTHER INCOME (EXPENSE).......     (2,954)    (2,736)    (3,677)   (10,995)
                                     ---------  ---------  ---------  ---------
LOSS BEFORE INCOME TAXES AND
 EXTRAORDINARY LOSSES..............    (13,286)    (7,913)   (33,416)   (30,836)
INCOME TAX BENEFIT.................        195      1,955        942      4,934
                                     ---------  ---------  ---------  ---------
LOSS BEFORE EXTRAORDINARY LOSSES...    (13,091)    (5,958)   (32,474)   (25,902)
EXTRAORDINARY LOSS ON
 EXTINGUISHMENT OF DEBT, NET OF
 INCOME TAX BENEFIT OF $921........                                      (1,382)
EXTRAORDINARY LOSS ON REDEMPTION OF
 INTERIM PREFERRED STOCK, NET OF
 INCOME TAX BENEFIT OF $5,000......                (7,510)               (7,510)
                                     ---------  ---------  ---------  ---------
NET LOSS...........................  $ (13,091) $ (13,468) $ (32,474) $ (34,794)
                                     =========  =========  =========  =========

BASIC AND DILUTED NET LOSS PER
 COMMON SHARE AMOUNTS--
 Loss Before Extraordinary
  Losses...........................  $    (.08) $    (.06) $    (.22) $    (.37)
 Extraordinary Losses..............                  (.07)                 (.13)
                                     ---------  ---------  ---------  ---------
NET LOSS...........................  $    (.08) $    (.13) $    (.22) $    (.50)
                                     =========  =========  =========  =========
WEIGHTED AVERAGE NUMBER OF COMMON
 SHARES OUTSTANDING................    155,625    104,621    147,588     70,103
                                     =========  =========  =========  =========
</TABLE>


           See notes to condensed consolidated financial statements.

                                       4
<PAGE>

                  AMERICAN TOWER CORPORATION AND SUBSIDIARIES

           CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS--UNAUDITED
                                 (In thousands)

<TABLE>
<CAPTION>
                                                           Nine Months Ended
                                                             September 30,
                                                          --------------------
                                                            1999       1998
                                                          ---------  ---------
<S>                                                       <C>        <C>
CASH FLOWS PROVIDED BY OPERATING ACTIVITIES.............. $  56,561  $   2,878
                                                          ---------  ---------
CASH FLOWS USED FOR INVESTING ACTIVITIES:
  Payments for purchase of property and equipment and
   construction in progress..............................  (173,864)   (76,291)
  Payments for acquisitions, net of cash acquired........  (361,256)  (140,384)
  Advances of notes receivable...........................   (64,488)   (11,100)
  Proceeds from notes receivable.........................       538      2,000
  Deposits, investments and other long-term assets.......  (137,693)    (2,140)
                                                          ---------  ---------
Cash used for investing activities.......................  (736,763)  (227,915)
                                                          ---------  ---------
CASH FLOWS FROM FINANCING ACTIVITIES:
  Borrowings under notes payable and credit facilities...    95,357    205,500
  Repayment of notes payable and credit facilities.......  (143,233)  (136,954)
  Net proceeds from equity offerings and stock options...   634,293    707,399
  Cash transfers to CBS Corporation......................   (50,000)  (221,665)
  Net proceeds from Interim Preferred Stock..............              300,000
  Redemption of Interim Preferred Stock..................             (303,117)
  Contributions from ARS.................................               56,954
  Cash transfers to ARS..................................              (51,856)
  Distributions to minority interest.....................      (315)      (314)
  Deferred financing costs...............................      (364)   (22,052)
                                                          ---------  ---------
Cash provided by financing activities....................   535,738    533,895
                                                          ---------  ---------
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS.....  (144,464)   308,858
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD...........   186,175      4,596
                                                          ---------  ---------
CASH AND CASH EQUIVALENTS, END OF PERIOD................. $  41,711  $ 313,454
                                                          =========  =========
CASH PAID FOR INCOME TAXES............................... $   1,401  $     239
                                                          =========  =========
CASH PAID FOR INTEREST................................... $  16,006  $  16,036
                                                          =========  =========
NON-CASH TRANSACTIONS:
  Contribution of property and equipment and other assets
   from ARS..............................................            $   6,488
  Issuance of common stock and assumption of options for
   acquisitions.......................................... $ 448,037  $ 363,609
  Increase in deferred tax assets from corporate
   restructuring.........................................            $ 135,000
  (Decrease) increase in due to CBS Corporation from
   estimated remaining tax liabilities................... $  (7,813) $ 131,660
  Escrow return -- treasury stock........................ $   1,528
</TABLE>

           See notes to condensed consolidated financial statements.

                                       5
<PAGE>

                  AMERICAN TOWER CORPORATION AND SUBSIDIARIES

        NOTES TO CONDENSED CONSOLIDATED FINANCIAL STATEMENTS--UNAUDITED

1. Basis of Presentation and Accounting Policies

  The accompanying condensed consolidated financial statements have been
prepared by American Tower Corporation (the Company or American Tower),
without audit, pursuant to the rules and regulations of the Securities and
Exchange Commission (SEC). The financial information included herein is
unaudited; however, the Company believes such information and the disclosures
are adequate to make the information presented not misleading. In addition,
the Company believes such information reflects all adjustments (consisting
only of normal recurring adjustments) that are necessary for a fair
presentation of financial position and results of operations for such periods.
Results of interim periods may not be indicative of results for the full year.
These condensed consolidated financial statements and related notes should be
read in conjunction with the Company's 1998 Annual Report on Form 10-K and
interim reports on Form 10Q for the three month periods ended March 31, 1999
and June 30, 1999 filed with the SEC on March 19, 1999, May 17, 1999 and
August 16, 1999, respectively.

  Use of Estimates--The preparation of financial statements in conformity with
generally accepted accounting principles requires management to make estimates
and assumptions that affect the amounts reported in the condensed consolidated
financial statements and accompanying notes. Actual results may differ from
those estimates, and such differences could be material to the accompanying
condensed consolidated financial statements.

  Loss Per Common Share--Basic and diluted income or loss per common share
have been determined in accordance with Statement of Financial Accounting
Standards (FAS) No. 128, "Earnings Per Share," whereby basic income or loss
per common share is computed by dividing net income or loss by the weighted
average number of common shares outstanding during the period. Diluted per
share amounts are computed by adjusting the weighted average number of common
shares for dilutive potential common shares outstanding during the period, if
any. In computing diluted per share amounts, the Company uses the treasury
stock method, whereby unexercised options are assumed to be exercised at the
beginning of the period or at issuance, if later. The assumed proceeds are
then used to purchase common shares at the average market price during the
period. Shares outstanding upon the consummation of the ATC Separation (as
defined in note 2 below) are assumed to be outstanding for all periods prior
to June 4, 1998. Shares issuable upon exercise of options have been excluded
from the computation of diluted income or loss per common share as the effect
is anti-dilutive. Had options been included in the computation, shares for the
diluted computation would have increased by approximately 5.0 and 5.4 million
and 4.4 and 4.0 million for the three and nine month periods ended September
30, 1999 and 1998, respectively.

  Tower Separation Expense--Tower separation expense consists of one-time
costs incurred in connection with the separation of the Company from its
former parent and includes legal, accounting, financial advisory and consent
solicitation fees.

  Recent Accounting Pronouncement--In June 1998, the Financial Accounting
Standards Board (FASB) issued Statement of Financial Accounting Standards
(FAS) No. 133, Accounting for Derivative Instruments and Hedging Activities,
as amended in May 1999 by FAS No. 137. This statement establishes accounting
and reporting standards for derivative instruments. It requires that an entity
recognize all derivatives as either assets or liabilities in the statement of
financial position, and measure those instruments at fair value. The
accounting for changes in the fair value of a derivative (that is, gains and
losses) will depend on the entity's intended use of the derivative and its
resulting designation (as defined in the statement). FAS No. 133, as amended,
is effective for all fiscal quarters of all fiscal years beginning after
January 1, 2000. The Company is currently in the process of evaluating the
impact FAS No. 133 will have on the Company and its consolidated financial
statements.

  Reclassifications--Certain reclassifications have been made to the 1998
condensed consolidated financial statements to conform to the 1999
presentation.

                                       6
<PAGE>

                  AMERICAN TOWER CORPORATION AND SUBSIDIARIES

       NOTES TO CONDENSED CONSOLIDATED FINANCIAL STATEMENTS--(UNAUDITED)

2. ATC Separation

  As disclosed in the Company's 1998 Annual Report on Form 10-K, the Company
was formerly a wholly-owned subsidiary of American Radio Systems Corporation
(ARS) until its spin-off from ARS on June 4, 1998 (the ATC Separation). As
part of the ATC Separation, the Company was required to reimburse CBS
Corporation (CBS) for certain tax liabilities incurred by ARS as a result of
the transaction. As of December 31, 1998 the Company had made estimated tax
payments to CBS of approximately $212.0 million. The Company was also required
to make additional payments to CBS upon the conversion of ARS 7% Convertible
Debentures (the ARS Convertible Debentures) by the holders thereof as these
conversions were expected to increase ARS's ultimate tax liability. In the
third quarter of 1999, the remaining holders of the ARS Convertible Debentures
elected to convert their holdings. Upon such conversion and the completion of
the 1998 ARS tax return, a final calculation of the total tax payments due
from CBS was performed by CBS. Such calculation reflected a refund to the
Company of amounts previously paid of approximately $2.8 million, which is
subject to review by the Company before final settlement. Such amount along
with the Company's previously provided security deposit of $9.8 million are
recorded as "Due from CBS" in the accompanying September 30, 1999 condensed
consolidated balance sheet. The Company continues to be obligated to indemnify
CBS and ARS for certain tax matters affecting ARS prior to the ATC Separation.
As of September 30, 1999, no such matters have been brought to the Company's
attention. See the Company's 1998 Annual Report on Form 10-K and the March 31,
1999 and June 30, 1999 quarterly reports on Form 10-Q for a more detailed
discussion related to the ATC Separation.

3. Significant Customers

  For the three and nine month periods ended September 30, 1999, one customer
accounted for approximately 16%, of the Company's consolidated revenues. No
single customer accounted for more than 10% of consolidated revenues during
the three or nine month periods ended September 30, 1998.

4. Income Taxes

  The Company provides for income taxes at the end of each interim period
based on the estimated effective tax rate for the full fiscal year. Cumulative
adjustments to the Company's estimate are recorded in the interim period in
which a change in the estimated annual effective rate is determined.

5. Stockholders' Equity

  Redeemable Common Stock: In June 1998, the Company merged with a company
owning a broadcasting tower in the Boston, Massachusetts area and issued
720,000 shares of Class A common stock valued at approximately $18.0 million.
Under a put agreement that was executed in connection with the merger, the
sellers had the right to require the Company to purchase, at any time prior to
June 5, 1999, any or all shares of Class A common stock received pursuant to
consummation of the merger for a purchase price equal to the then current
market price. On June 5, 1999, the sellers' right to require the Company to
purchase shares of common stock expired. Accordingly all unsold shares as of
that date (383,750) were reclassified from Redeemable Class A common stock to
common stock and additional paid in capital.

  Secondary Public Offering: In February 1999, the Company completed a
secondary public offering of 25,700,000 shares of Class A common stock, $.01
par value per share (including 1,700,000 shares sold by the Company pursuant
to the exercise in full of the underwriters' over-allotment option) at $25.00
per share. Certain selling stockholders sold an additional 1,300,000 shares in
the offering. The Company's net proceeds of the

                                       7
<PAGE>

                  AMERICAN TOWER CORPORATION AND SUBSIDIARIES

       NOTES TO CONDENSED CONSOLIDATED FINANCIAL STATEMENTS--(UNAUDITED)

offering (after deduction of the underwriting discount and offering expenses)
were approximately $618.0 million. The Company initially invested the proceeds
in short-term investment grade securities. The Company used such proceeds,
together with borrowings under its existing credit facilities, to fund
acquisitions and construction activities.

  Private Placement: In February 1999, the Company consummated the sale of
500,000 shares of Class A common stock to Credit Suisse First Boston
Corporation at $26.31 per share. In connection with such sale, Credit Suisse
First Boston Corporation was granted certain registration rights. The Company
initially invested the proceeds of approximately $13.1 million in short-term
investment grade securities. The Company used such proceeds, together with
borrowings under its existing credit facilities, to fund acquisitions and
construction activities.

  Other Changes to Stockholders' Equity: See note 6 of the condensed
consolidated financial statements for issuances of common stock in connection
with the Company's acquisitions consummated during the nine month period ended
September 30, 1999.

6. Acquisitions

  General--The acquisitions consummated during the nine month period ended
September 30, 1999 have been accounted for using the purchase method of
accounting. The purchase prices related to these acquisitions have been
allocated to the net assets acquired based on their estimated fair value at
the date of acquisition. The excess of purchase price over the estimated fair
value of the net assets acquired has been recorded as goodwill and other
intangible assets. For certain acquisitions, the condensed consolidated
financial statements reflect the preliminary allocation of purchase prices as
the appraisals related to the net assets acquired have not been finalized. The
Company does not expect any changes in depreciation and amortization, as a
result of such appraisals, to be material to the consolidated results of
operations.

 Consummated Transactions

  The following provides a general description of the significant transactions
consummated during the nine-month period ended September 30, 1999:

  Omni Merger--In February 1999, the Company consummated the Agreement and
Plan of Merger, dated as of November 16, 1998 (the Omni Merger) with
OmniAmerica, Inc. (Omni). Omni owned, managed and constructed multi-use
telecommunications sites for radio and television broadcasting, paging,
cellular, PCS and other wireless technologies and offered nationwide, turn-key
tower construction and installation services. Pursuant to the Omni Merger
agreement, Omni stockholders received 1.1 shares of the Company's Class A
common stock for each share of Omni common stock. In the aggregate, the
Company exchanged approximately 16.8 million shares of Class A common stock
for approximately 15.2 million shares of Omni common stock. In addition, the
Company assumed $96.6 million of debt, of which $94.3 million (inclusive of
interest and fees) was paid at closing. The Company also assumed certain Omni
employee stock options which were converted into options to purchase
approximately 1.0 million shares of the Company's Class A common stock. Total
merger consideration was approximately $462.0 million.

  TeleCom Merger--In February 1999, the Company consummated the Agreement and
Plan of Merger, dated as of November 16, 1998 (the TeleCom Merger) with
TeleCom Towers, L.L.C. (TeleCom). Telecom owned or co-owned approximately 271
towers and managed 121 revenue-generating sites in 27 states. Total merger
consideration of approximately $194.6 million included the issuance of 3.9
million shares of Class A common stock, payment of $63.1 million in cash and
the assumption of $48.4 million of debt.


                                       8
<PAGE>

                  AMERICAN TOWER CORPORATION AND SUBSIDIARIES

       NOTES TO CONDENSED CONSOLIDATED FINANCIAL STATEMENTS--(UNAUDITED)

  Comm Site Merger--In June 1999, the Company consummated the Agreement and
Plan of Merger, dated as of May 13, 1999 (the Comm Site Merger) with Comm Site
International, Inc. (Comm Site). The merger with Comm Site, a company that
specialized in antenna site development and site management, is expected to
expand the Company's presence in the Midwest and Southeast regions of the
United States. Total cash consideration paid by the Company in connection with
the Comm Site Merger was approximately $25.6 million, subject to a closing
balance sheet working capital adjustment, which is expected to be finalized in
the fourth quarter of 1999. The impact of the working capital adjustment is
not expected to be material to the Company's consolidated financial
statements.

  Triton PCS Acquisition--In September 1999, the Company consummated the
acquisition of 187 wireless communications towers from Triton PCS, the first
member of the AT&T Wireless Network, for $71.0 million in cash. Five
additional communications towers are expected to be purchased from Triton PCS
in the fourth quarter of 1999 for $1.9 million in cash. The towers are located
in Georgia, North Carolina, South Carolina and Virginia. In addition, the
Company agreed to develop a minimum of 100 build-to-suit towers for Triton PCS
and provide turnkey services to Triton PCS for co-location sites through 2001.

  In addition to the above, the Company also consummated a number of other
tower related asset purchases during the nine month period ended September 30,
1999. Total consideration paid in connection with these transactions was
approximately $194.5 million.

  The following unaudited pro forma summary for the nine months ended
September 30, 1999 and 1998 presents the condensed consolidated results of
operations as if the 1999 acquisitions discussed above had occurred as of
January 1, 1998 after giving effect to certain adjustments, including
depreciation and amortization of assets and interest expense on any debt
incurred to fund the acquisitions. These unaudited pro forma results have been
prepared for comparative purposes only and do not purport to be indicative of
what would have occurred had the acquisitions been made as of January 1, 1998
or of results that may occur in the future.

In thousands, except per share data:

<TABLE>
<CAPTION>
                                            Nine Months        Nine Months
                                               Ended              Ended
                                         September 30, 1999 September 30, 1998
                                         ------------------ ------------------
      <S>                                <C>                <C>
      Revenues..........................      $206,130           $162,702
      Loss before extraordinary items...      $(43,040)          $(48,071)
      Net loss..........................      $(43,040)          $(56,963)
      Basic and diluted net loss per
       common share.....................      $  (0.28)          $  (0.63)
</TABLE>

  Since October 1, 1999, the Company has acquired and made investments in
several communication sites and businesses for an aggregate preliminary
purchase price of approximately $59.6 million.

 Pending Transactions

  The following provides a general description of significant transactions
that are expected to be consummated in the fourth quarter of 1999 and into the
year 2000.

  AirTouch Communications Inc.--In August 1999, the Company signed a
definitive agreement with AirTouch Communications, Inc. (AirTouch), a unit of
Vodafone AirTouch PLC, to acquire the rights to approximately 2,100
communications towers through a master sublease agreement. In addition, the
Company will enter into an exclusive three-year build-to-suit agreement that
is expected to produce approximately 400-500 new communications towers. Total
consideration to be paid by the Company in connection with this transaction
includes approximately $800.0 million in cash, plus a five year warrant to
purchase 3.0 million shares of the

                                       9
<PAGE>

                  AMERICAN TOWER CORPORATION AND SUBSIDIARIES

       NOTES TO CONDENSED CONSOLIDATED FINANCIAL STATEMENTS--(UNAUDITED)

Company's Class A common stock at $22.00 per share. The cash portion of the
consideration to be paid in connection with this transaction is expected to
come from a combination of current available funds, additional borrowings
under its credit facilities or proceeds from the sale of the Company's
issuance of convertible notes (described in note 8 below). The transaction is
expected to close incrementally, beginning in the first quarter of 2000,
subject to certain conditions.

  AT&T transaction--In September 1999, the Company signed a definitive
agreement with AT&T Corp. to purchase 1,942 towers. The towers are located
throughout the United States and were constructed by AT&T for its microwave
operations. In addition, the Company agreed to enter into a build-to-suit
agreement with AT&T Wireless Services at the initial closing of the
transaction that is expected to produce the opportunity to build 1,000 towers.
The purchase price for this transaction is $260.0 million in cash, subject to
adjustment if all towers are not purchased. At the initial closing, AT&T will
enter into a master lease agreement covering all towers in which it conducts
microwave operations. The lease will have an initial term of ten years, and
AT&T will have five, five-year renewal options. AT&T currently uses 468 of
these towers for its microwave operations. It is expected that as many as 50%
of the towers may not be marketable in the near future because of location.
There will be a separate master lease with AT&T Wireless Services for the
build-to-suit towers. The initial term will be ten years, and AT&T will have
three, five-year renewals. The transaction will be closed in stages, subject
to the satisfaction of customary conditions, including the receipt of all
regulatory approvals, beginning in the fourth quarter of 1999 or the first
quarter of 2000.

  UNIsite Merger--In June 1999, the Company entered into an Agreement and Plan
of Merger (the UNIsite Merger) with UNIsite, Inc. (UNIsite). UNIsite, whose
primary focus has been tower site management, has recently expanded its scope
of services to include site ownership and development. Presently, UNIsite owns
approximately 400 towers and has an exclusive build-to-suit agreement with a
major wireless communications carrier. Pursuant to the UNIsite Merger
agreement, UNIsite preferred and common stockholders will receive an aggregate
of approximately $165.0 million in cash, subject to working capital and
completed tower closing adjustments. In addition, the Company will assume
approximately $40.0 million in debt. Consummation of the merger is expected to
occur on the earlier of (a) January 31, 2000, or (b) UNIsite owning and
operating 600 wireless communication towers, subject to certain conditions.

  TV Azteca Transaction--In September 1999, the Company entered into a letter
of intent with TV Azteca, the owner of a major national television broadcast
network in Mexico, relating to approximately 200 broadcast towers. The Company
agreed to loan up to $120.0 million to that company and to take over
responsibility for marketing and certain maintenance functions for the towers.
The 20-year loan, which may be extended for an additional 20 years, will bear
net interest at approximately 11.0% per annum, subject to certain conditions.
The Company will be entitled to receive 100% of the revenues generated by
third party leases on the towers during the term of the loan. The closing is
subject to certain conditions, including the execution and delivery of
definitive agreements and the receipt of all necessary regulatory approvals.
Subject to satisfaction of those conditions, definitive agreements are
scheduled to be executed in the fourth quarter of 1999.

  In connection with the TV Azteca letter of intent, on September 15, 1999,
the Company entered into a six month credit agreement (interim financing)
whereby the Company will advance $60.0 million to TV Azteca. The interim
financing will bear interest at 11.0% payable quarterly, and is partially
collaterized by the American Depository Shares of TV Azteca. As of September
30, 1999 the Company had advanced $32.0 million under the interim financing
agreement. The remaining $28.0 million was advanced in October 1999.

  ICG Satellite Services Merger--In August 1999, the Company entered into a
Stock Purchase Agreement with ICG Satellite Services, Inc. (ICGSS) to acquire
a teleport facility and global maritime telecommunications network. Presently,
ICGSS services voice, data internet and compressed video via satellite to
major cruise lines, the U.S. Military, internet-related companies and
international telecommunication customers. Total cash

                                      10
<PAGE>

                  AMERICAN TOWER CORPORATION AND SUBSIDIARIES

       NOTES TO CONDENSED CONSOLIDATED FINANCIAL STATEMENTS--(UNAUDITED)
consideration to be paid by the Company in connection with this merger is
approximately $100.0 million. The transaction is expected to close in the
fourth quarter of 1999, subject to the satisfaction of customary conditions.

  Watson Acquisition--In July 1999, the Company entered into an agreement to
acquire Watson Communications for $73.0 million in cash. The acquisition
involves 11 wireless and 10 broadcast towers in the San Francisco Bay area and
one teleport containing nine antennas. The teleport covers the full domestic
and the pacific international service region. Among the acquired sites is San
Bruno Mountain, a premiere location within the San Francisco market. The
transaction is expected to close in the fourth quarter of 1999, subject to the
satisfaction of customary conditions.

  In addition to the above agreements, the Company is party to various
agreements relating to the acquisition of assets from third parties for an
estimated aggregate cost of approximately $28.2 million. Such transactions are
subject to the satisfaction of customary closing conditions, which are
expected to be met in the last quarter of 1999 or the first quarter of 2000.

7. Business Segments

  The Company operates in three business segments; rental and management (RM),
services (Services), and video, voice, data and Internet transmission (VVDI).
The RM segment primarily provides for leasing and subleasing of antennae sites
on multi-tenant towers for a diverse range of wireless communication
industries, including personal communication services, paging, cellular,
enhanced specialized mobile radio, specialized mobile radio and fixed
microwave, as well as radio and television broadcasters. The Services segment
offers a broad range of network development services, including network
design, site acquisition and construction, zoning and other regulatory
approvals, component part sales, tower construction and antennae installation.
The VVDI segment offers transmission services in the New York City to
Washington, D.C. corridor and in Texas.

  The accounting policies applied in compiling segment information below are
similar to those described in the Company's 1998 Annual Report filed on Form
10-K and interim reports on Form 10-Q for the quarterly periods ended March
31, 1999 and June 30, 1999, respectively. In evaluating financial performance,
management focuses on Operating Profit (Loss), which excludes depreciation and
amortization, tower separation and corporate general and administrative
expenses. This measure of Operating Profit (Loss) is also before interest
income and other, net, interest expense, minority interest in net (earnings)
losses of subsidiaries and income taxes.

  The Company's reportable segments are strategic business units that offer
different services. They are managed separately because each segment requires
different resources, skill sets and marketing strategies. All segments operate
exclusively in the United States. In addition, all reported segment revenues
are generated from external customers, as intersegment revenues are
insignificant.


                                      11
<PAGE>

                  AMERICAN TOWER CORPORATION AND SUBSIDIARIES

       NOTES TO CONDENSED CONSOLIDATED FINANCIAL STATEMENTS--(UNAUDITED)
  Summarized financial information concerning the Company's reportable
segments as of and for the three and nine months ended September 30, 1999 and
1998, are shown in the following table. The "Other" column below represents
amounts excluded from specific segments such as extraordinary losses, income
taxes, corporate general and administrative expense, tower separation expense,
depreciation and amortization and interest. In addition, "Other" also includes
corporate assets such as cash and cash equivalents, tangible and intangible
assets, and income tax accounts, which have not been allocated to specific
segments (in thousands).

<TABLE>
<CAPTION>
Three Months Ended
September 30,                    RM     Services  VVDI     Other      Total
- ------------------           ---------- -------- ------- ---------  ----------
<S>                          <C>        <C>      <C>     <C>        <C>
1999
Revenues...................  $   37,768 $ 22,710 $ 7,061            $   67,539
Operating Profit (Loss)....  $   19,851 $  5,600 $ 1,583 $ (40,125) $  (13,091)
Assets.....................  $1,630,886 $489,207 $92,229 $ 408,236  $2,620,558
1998
Revenues...................  $   17,719 $  6,572 $ 6,187            $   30,478
Operating Profit (Loss)....  $    9,632 $  1,895 $ 2,259 $ (27,254) $  (13,468)
Assets.....................  $  820,043 $113,829 $72,939 $ 428,943  $1,435,754
<CAPTION>
Nine Months Ended September
30,                              RM     Services  VVDI     Other      Total
- ---------------------------  ---------- -------- ------- ---------  ----------
<S>                          <C>        <C>      <C>     <C>        <C>
1999
Revenues...................  $   94,640 $ 54,948 $19,512            $  169,100
Operating Profit (Loss)....  $   51,152 $ 13,153 $ 5,270 $(102,049) $  (32,474)
Assets.....................  $1,630,886 $489,207 $92,229 $ 408,236  $2,620,558
1998
Revenues...................  $   39,305 $ 18,848 $13,332            $   71,485
Operating Profit (Loss)....  $   20,888 $  3,436 $ 4,635 $ (63,753) $  (34,794)
Assets.....................  $  820,043 $113,829 $72,939 $ 428,943  $1,435,754
</TABLE>

8. Private Notes Placement

  On October 4, 1999 the Company completed a private notes placement of $300.0
million principal amount of 6.25% Convertible Notes due 2009 (6.25% Notes),
issued at 100% of their face amount, and $425.5 million principal amount of
2.25% Convertible Notes due 2009 (2.25% Notes), issued at 70.52% of their face
amount. Total net proceeds received from the private placement notes were
approximately $584.0 million. The 6.25% Notes are convertible, at the option
of the holder, into the Company's Class A common stock at a conversion price
of $24.40 per share. The 2.25% Notes are convertible, at the option of the
holder, into Class A common stock at a conversion price of $24.00 per share.
Approximately $368.0 million of the net proceeds from the private placement
notes were used to pay off borrowings under the Company's existing credit
facility. The remaining portion of the proceeds will be used to finance
acquisitions and construction.

  On October 20, 1999, the Company filed a registration statement on Form S-3
to register the resale of the 6.25% and the 2.25% Notes by the holders
thereof. Such registration statement was declared effective on November 2,
1999.

                                      12
<PAGE>

ITEM 2. MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND
        RESULTS OF OPERATIONS

General

  This discussion contains forward-looking statements, including statements
concerning projections, plans, objectives, future events or performance and
underlying assumptions and other statements, which are other than statements
of historical fact. Various factors affect the Company's results and could
cause the Company's actual results to differ materially from those expressed
in any forward-looking statement. Such factors include:

  .  the outcome of our growth strategy,
  .  future results of operations,
  .  liquidity and capital expenditures,
  .  construction and acquisition activities,
  .  debt levels and the ability to obtain financing and service debt,
  .  competitive conditions and regulatory developments in the communications
     site and wireless carrier industries,
  .  projected growth of the wireless communications and wireless carrier
     industries,
  .  dependence on demand for satellites for internet data transmission, and
  .  general economic conditions.

  As the Company was a wholly-owned subsidiary of ARS through June 4, 1998,
the condensed consolidated financial statements for the three and nine months
ended September 30, 1998 may not reflect the results of operations or
financial position of the Company had it been an independent public company
during such periods. Because of the Company's relatively brief operating
history and the large number of recent acquisitions, the following discussion
will not necessarily reveal all significant developing or continuing trends.

  The Company is a leading independent owner, operator and developer of
wireless communications towers in the United States. From January 1, 1999
through September 30, 1999, the Company acquired various communications sites
and businesses for an aggregate estimated purchase price of approximately
$948.3 million, which includes cash paid, the assumption of debt and the
issuance of approximately 20.7 million shares of Class A common stock.
Management expects that acquisitions consummated to date and in the future
will have a material impact on future revenues, expenses and results from
operations.

Results of Operations

  As of September 30, 1999, the Company owned and/or operated approximately
4,600 communications sites, as compared to approximately 1,900 communications
sites as of September 30, 1998. The acquisitions consummated in 1999 and 1998
have significantly affected operations for the three and nine months ended
September 30, 1999, as compared to the three and nine months ended September
30, 1998. See the notes to the condensed consolidated financial statements for
a description of the acquisitions consummated in 1999 and the Company's Annual
Report on Form 10-K for acquisitions consummated in 1998 and prior.

                                      13
<PAGE>

Three months ended September 30, 1999 and 1998 (Dollars in thousands)--
Unaudited

<TABLE>
<CAPTION>
                                    Three months ended    Amount of  Percentage
                                       September 30,
                                    --------------------   Increase   Increase
                                      1999       1998     (Decrease) (Decrease)
                                    ---------  ---------  ---------- ----------
<S>                                 <C>        <C>        <C>        <C>
  Revenues:
  Rental and management............ $  37,768  $  17,719   $20,049       113%
  Services.........................    22,710      6,572    16,138       246%
  Video, voice, data and Internet
   transmission....................     7,061      6,187       874        14%
                                    ---------  ---------   -------
  Total revenues...................    67,539     30,478    37,061       122%
                                    ---------  ---------   -------
  Operating Expenses:
  Rental and management............    17,917      8,087     9,830       122%
  Services.........................    17,110      4,677    12,433       266%
  Video, voice, data and Internet
   transmission....................     5,478      3,928     1,550        39%
                                    ---------  ---------   -------
  Total operating expenses exclud-
   ing depreciation and
   amortization, tower separation,
   and corporate general and admin-
   istrative expenses..............    40,505     16,692    23,813       143%
                                    ---------  ---------   -------
  Depreciation and amortization....    35,111     17,243    17,868       104%
  Tower separation expense.........                  159      (159)     (100%)
  Corporate general and administra-
   tive expense....................     2,255      1,561       694        44%
  Interest expense.................     5,958      7,121    (1,163)      (16%)
  Interest income and other, net...     3,162      4,451    (1,289)      (29%)
  Minority interest in net earnings
   of subsidiaries.................       158         66        92       139%
  Income tax benefit...............       195      1,955    (1,760)      (90%)
  Extraordinary loss on redemption
   of interim preferred stock,
   net.............................                7,510    (7,510)     (100%)
                                    ---------  ---------   -------
  Net loss......................... $ (13,091) $ (13,468)  $  (377)       (3%)
                                    =========  =========   =======
</TABLE>

 Rental and Management Revenue

  Rental and management revenue for the three months ended September 30, 1999,
was $37.8 million, an increase of $20.0 million from the three months ended
September 30, 1998. The majority of the increase, $18.0 million, is
attributable to revenue generated from acquisitions consummated and/or towers
constructed subsequent to September 30, 1998. The remaining factor
contributing to the additional revenue is an increase in comparable tower
revenue of $2.0 million in the third quarter of 1999 for towers that existed
in the third quarter of 1998.

 Services Revenue

  Services revenue for the three months ended September 30, 1999, was $22.7
million, an increase of $16.1 million from revenues for the three months ended
September 30, 1998. The primary reason for the increase is due to the $17.5
million of revenue earned in the third quarter of 1999 from operations
acquired in the Omni Merger. The increase from the Omni Merger is offset by a
decrease in revenues generated from the Company's existing services business
of approximately $1.4 million. This decrease is a direct result of the
Company's shift in focus on site acquisition, development and construction of
towers for its own use ("Build-to-Suit") from its previous focus on
development and construction of towers for sale to third parties.

                                      14
<PAGE>

 Video, Voice, Data and Internet Transmission Revenue

  Video, voice, data and Internet transmission (VVDI) revenue for the three
months ended September 30, 1999, was $7.1 million, an increase of $0.9 million
from revenues for the three months ended September 30, 1998. The primary
reason for the increase is attributed to approximately $0.7 million of
revenues earned during the current period as a result of an acquisition that
closed in July of 1999. The remaining component of the increase, $0.2 million,
is due to growth in the overall VVDI business that existed at September 30,
1998.

 Rental and Management, Services and VVDI Expenses

  Rental and management, Services and VVDI expenses for the three months ended
September 30, 1999, were $17.9 million, $17.1 million and $5.5 million,
respectively, an increase of $9.8 million, $12.4 million and $1.6 million,
respectively, from the three months ended September 30, 1998. The primary
reasons for the increase in these expenses are essentially the same as those
discussed above under each respective revenue segment.

 Depreciation and Amortization

  Depreciation and amortization for the three months ended September 30, 1999,
was $35.1 million, an increase of $17.9 million from the three months ended
September 30, 1998. A component of the increase is attributable to an increase
in depreciation expense of $7.6 million. This is a direct result of the
Company's purchase, construction and/or acquisition of approximately $547.8
million of property and equipment from October 1, 1998 to September 30, 1999.
The remaining component of the increase is attributable to an increase in
amortization of $10.3 million, resulting from the Company's recording and
amortizing of approximately $668.9 million of goodwill and other intangible
assets related to acquisitions consummated from October 1, 1998 to September
30, 1999.

 Tower Separation Expense

  The Company completed its separation from ARS in the second quarter of 1998,
and incurred minimal additional expenses related to the separation in the
third quarter of 1998. No additional expenses related to the separation were
incurred in the three month period ended September 30, 1999, or are expected
to occur in the future. See note 1 of the condensed consolidated financial
statements for a description of tower separation expense.

 Corporate General and Administrative Expense

  Corporate general and administrative expense for the three months ended
September 30, 1999, was $2.3 million, an increase of $0.7 million from the
three months ended September 30, 1998. The majority of the increase is a
result of higher personnel and marketing costs associated with supporting the
Company's expanding revenue base and market position. The remaining component
of the increase is attributed to overall increases to other administrative
expenses.

 Interest Expense

  Interest expense for the three months ended September 30, 1999, was $6.0
million, a decrease of $1.2 million from the three months ended September 30,
1998. The net decrease is attributable to a decrease in the current period of
approximately $0.8 million of interest incurred in 1998 on outstanding
redeemable preferred stock which was redeemed prior to 1999, coupled with an
increase in interest capitalized during the three month period ended September
30, 1999 as a result of increased construction activity.

                                      15
<PAGE>

 Interest Income and Other, Net

  Interest income and other, net for the three months ended September 30,
1999, was $3.2 million, a decrease of $1.3 million from the three months ended
September 30, 1998. The decrease is primarily related to a decrease in
interest earned on invested cash on hand offset by an increase in interest
earned on notes receivable and security deposits.

 Income Tax Benefit

  The income tax benefit for the three months ended September 30, 1999 was
$0.2 million, a decrease of $1.8 million from the income tax benefit recorded
for the three months ended September 30, 1998. In addition, the effective
income tax benefit rate for the three months ended September 30, 1999 was 2%,
as compared to an effective income tax benefit rate of 25% for the three
months ended September 30, 1998. The decrease in the tax benefit and the
effective tax benefit rate is due to an increase in nondeductible permanent
items (principally goodwill amortization). The increase in nondeductible
permanent items has occurred as a result of the consummation of several
mergers and acquisitions in 1999 and the latter part of 1998.

 Extraordinary Loss on Extinguishment of Debt

  The Company incurred an extraordinary loss in 1998 due to the redemption of
its interim preferred stock. There have been no transactions that qualify for
treatment as extraordinary items during the three month period ended September
30, 1999.

                                      16
<PAGE>

Nine months ended September 30, 1999 and 1998 (Dollars in thousands)--
Unaudited

<TABLE>
<CAPTION>
                                       Nine Months Ended
                                         September 30,     Amount of  Percentage
                                       ------------------  Increase    Increase
                                         1999      1998    (Decrease) (Decrease)
                                       --------  --------  ---------  ----------
<S>                                    <C>       <C>       <C>        <C>
Revenues:
Rental and management................  $ 94,640  $ 39,305   $55,335       141%
Services.............................    54,948    18,848    36,100       192%
Video, voice, data and Internet
 transmission........................    19,512    13,332     6,180        46%
                                       --------  --------   -------
Total revenues.......................   169,100    71,485    97,615       137%
                                       --------  --------   -------
Operating Expenses:
Rental and management................    43,488    18,417    25,071       136%
Services.............................    41,795    15,412    26,383       171%
Video, voice, data and Internet
 transmission........................    14,242     8,697     5,545        64%
                                       --------  --------   -------
Total operating expenses excluding
 depreciation and amortization, tower
 separation, and corporate general
 and administrative expenses.........    99,525    42,526    56,999       134%
                                       --------  --------   -------
Depreciation and amortization........    92,919    32,998    59,921       182%
Tower separation expense.............              12,616   (12,616)     (100%)
Corporate general and administrative
 expense.............................     6,395     3,186     3,209       101%
Interest expense.....................    17,497    17,023       474         3%
Interest income and other, net.......    13,899     6,283     7,616       121%
Minority interest in net earnings of
 subsidiaries........................        79       255      (176)      (69%)
Income tax benefit...................       942     4,934    (3,992)      (81%)
Extraordinary loss on extinguishment
 of debt, net........................               1,382    (1,382)     (100%)
Extraordinary loss on redemption of
 interim preferred stock, net........               7,510    (7,510)     (100%)
                                       --------  --------   -------
Net loss.............................  $(32,474) $(34,794)  $(2,320)       (7%)
                                       ========  ========   =======
</TABLE>

 Rental and Management Revenue

  Rental and management revenue for the nine months ended September 30, 1999,
was $94.6 million, an increase of $55.3 million from the nine months ended
September 30, 1998. The majority of the increase, $38.2 million, is
attributable to revenue generated from acquisitions consummated and/or towers
constructed subsequent to September 30, 1998. The remaining factor
contributing to the additional revenue is an increase in comparable tower
revenue of $17.1 million in the nine month period ended September 30, 1999 for
towers that existed in the nine month period ended September 30, 1998.

 Services Revenue

  Services revenue for the nine months ended September 30, 1999, was $55.0
million, an increase of $36.1 million from revenues for the nine months ended
September 30, 1998. The primary reason for the increase is due to the $40.6
million of revenue earned in 1999 from operations acquired in the Omni Merger.
The increase from the Omni Merger is offset by a decrease in revenues
generated from the Company's existing services business of approximately $4.5
million. This decrease is a direct result of the Company's shift in focus on
Build-to-Suit activities from its previous focus on development and
construction of towers for sale to outside customers.

                                      17
<PAGE>

 Video, Voice, Data and Internet Transmission Revenue

  VVDI revenue for the nine months ended September 30, 1999, was $19.5
million, an increase of $6.2 million from revenues for the nine months ended
September 30, 1998. The primary reason for the increase is attributed to an
increase of approximately $4.4 million of revenues earned during the nine
month period September 30, 1999 as a result of the acquisition of Washington
International Teleport which closed in the second quarter of 1998. The
remaining components of the increase are attributed to approximately $0.7
million of revenue generated from an acquisition made in the third quarter of
1999 coupled with a $1.1 million increase in the overall VVDI business
existing at September 30, 1998.

 Rental and Management, Services and VVDI Expenses

  Rental and management, Services and VVDI expenses for the nine months ended
September 30, 1999, were $43.5 million, $41.8 million and $14.2 million,
respectively, an increase of $25.0 million, $26.4 million and $5.5 million,
respectively, from the nine months ended September 30, 1998. The primary
reasons for the increase in these expenses are essentially the same as those
discussed above under each respective revenue segment.

 Depreciation and Amortization

  Depreciation and amortization for the nine months ended September 30, 1999,
was $92.9 million, an increase of $59.9 million from the nine months ended
September 30, 1998. A component of the increase is attributable to an increase
in depreciation expense of $22.2 million. This is a direct result of the
Company's purchase, construction and/or acquisition of approximately $547.8
million of property and equipment from October 1, 1998 to September 30, 1999.
The remaining component of the increase is attributable to an increase in
amortization of $37.7 million, resulting from the Company's recording and
amortizing of approximately $668.9 million of goodwill and other intangible
assets related to acquisitions consummated from October 1, 1998 to September
30, 1999.

 Tower Separation Expense

  The Company completed its separation from ARS in the second quarter of 1998,
and incurred minimal additional expenses related to the separation in the
third quarter of 1998. No additional expenditures related to the separation
were incurred in the nine month period ended September 30, 1999, or are
expected to occur in the future. See note 1 of the condensed consolidated
financial statements for a description of tower separation expense.

 Corporate General and Administrative Expense

  Corporate general and administrative expense for the nine months ended
September 30, 1999, was $6.4 million, an increase of $3.2 million from the
nine months ended September 30, 1998. The majority of the increase is a result
of higher personnel and marketing costs associated with supporting the
Company's expanding revenue base and market position. Other factors
contributing to the increase include higher costs associated with enhancing
the Company's information technology infrastructure and overall increases in
other administrative expenses.

 Interest Expense

  Interest expense for the nine months ended September 30, 1999, was $17.5
million, an increase of $0.5 million from the nine months ended September 30,
1998. The net increase is attributable to an increase in the amount of
interest incurred on the Company's outstanding debt obligations of
approximately $5.1 million. This increase was offset by a decrease of
approximately $3.9 million related to interest incurred in 1998 on outstanding
redeemable preferred stock which was redeemed prior to 1999, coupled with an
increase in interest capitalized during 1999 as a result of increased
construction activity.


                                      18
<PAGE>

 Interest Income and Other, Net

  Interest income and other, net for the nine months ended September 30, 1999,
was $13.9 million, an increase of $7.6 million from the nine months ended
September 30, 1998. The increase is primarily related to interest earned on
invested cash on hand, notes receivable and security deposits.

 Income Tax Benefit

  The income tax benefit for the nine months ended September 30, 1999 was $0.9
million, a decrease of $4.0 million from the nine months ended September 30,
1998. In addition, the effective income tax benefit rate for the nine months
ended September 30, 1999 was 3% as compared to an effective income tax benefit
rate of 16% for the nine months ended September 30, 1998. The decrease in the
tax benefit and the effective tax benefit rate is due to an increase in
nondeductible permanent items (principally goodwill amortization). The
increase in nondeductible permanent items has arisen as a result of the
consummation of several mergers and acquisitions in 1999 and the latter part
of 1998.

 Extraordinary Loss on Extinguishment of Debt

  The Company incurred extraordinary losses in 1998 due to the write-off of
deferred financing costs in connection with the refinancing of its previous
credit facility and the redemption of its interim preferred stock. There have
been no transactions that qualify for treatment as extraordinary items during
the nine month period ended September 30, 1999.

Liquidity and Capital Resources

  The Company's liquidity needs arise from its acquisition-related activities,
debt service, working capital and capital expenditures associated principally
with its construction program. As of September 30, 1999, the Company
maintained approximately $41.7 million in cash and cash equivalents and
working capital of approximately $42.0 million. In addition, the Company has
approximately $483.0 million available under its credit facilities.
Historically, the Company has met its operational liquidity needs with
internally generated funds and has financed the acquisition of tower related
properties and its construction program with a combination of capital funds
from sales of its equity securities and bank borrowings.

  For the nine months ended September 30, 1999, cash flows provided by
operating activities were $56.6 million, as compared to cash flows provided by
operating activities of $2.9 million for the nine months ended September 30,
1998. The change is primarily attributable to the favorable cash flow
generated from consummated acquisitions in 1999 and the latter part of 1998.

  For the nine months ended September 30, 1999, cash flows used for investing
activities were $736.8 million as compared to $227.9 million for the nine
months ended September 30, 1998. The increase in 1999 is primarily due to an
increase in property and equipment expenditures of approximately $95.6 million
coupled with the increase in cash expended for mergers and acquisitions,
including related escrow deposits, notes receivable and equity investments of
approximately $356.4 million.

  For the nine months ended September 30, 1999, cash flows provided by
financing activities were $535.7 million as compared to $533.9 million for the
nine months ended September 30, 1998. The net increase in 1999 is due
principally to a decrease in amounts transferred to CBS, offset by decreases
in borrowings under the Company's credit facilities and proceeds from equity
offerings.

  For the nine months ended September 30, 1999, the Company had capital
expenditures, exclusive of fixed assets acquired through acquisitions, of
approximately $173.9 million primarily related to construction activities,
including the completion of approximately 695 towers. The Company's 1999
business plan calls for construction of approximately 1,250 towers including
1,000 towers for its own account at a cost of between $180.0 million and
$200.0 million (exclusive of broadcast towers). Assuming the increase of its
credit facilities as described

                                      19
<PAGE>

below, management believes that the Company will have sufficient funds
available to finance current construction plans and pending acquisitions.
However, in the event that the Company was to negotiate more than one
additional major transaction, it would probably require additional financing
either through incurring additional debt or the sale of equity securities.
Such financing or sale of securities may not be available on favorable terms.

  Management expects that the consummated acquisitions and current and future
acquisitions and construction activities will have a material impact on
liquidity. Management believes that the acquisition activities, once
integrated, will have a favorable impact on liquidity and will offset the
initial effects of the funding requirements. Management also believes that the
construction activities may initially have an adverse effect on the future
liquidity of the Company as newly constructed towers will initially decrease
overall liquidity. But, as such sites become fully operational and achieve
higher utilization, they should generate positive cash flow, and, in the long-
term, increase liquidity.

  Private Placement Notes: On October 4, 1999 the Company completed a private
placement of $300.0 million principal amount of 6.25% Convertible Notes due
2009 (6.25% Notes), issued at 100% of their face amount, and $425.5 million
principal amount of 2.25% Convertible Notes due 2009 (2.25% Notes), issued at
70.52% of their face amount. Total net proceeds received from the private
placement notes were approximately $584.0 million. The 6.25% Notes are
convertible, at the option of the holder, into the Company's Class A common
stock at a conversion price of $24.40 per share. The 2.25% Notes are
convertible, at the option of the holder, into Class A common stock at a
conversion price of $24.00 per share.

  Approximately $368.0 million of the net proceeds from the private placement
notes were used to pay off borrowings under the Company's existing credit
facility. The remaining portion of the proceeds will be used to finance
acquisitions and construction.

  Credit Facilities: As of September 30, 1999, the Company had approximately
$378.6 million of debt, of which $368.0 million was outstanding in the form of
term loans and revolving credit facilities. Debt service requires a
substantial portion of the Company's cash flow from operations. Accordingly,
the Company's leverage could make it vulnerable to a downturn in the operating
performance of its tower properties or in economic conditions. The Company
believes that its cash flows from operations will be sufficient to meet its
debt service requirements for interest and scheduled payments of principal
under its existing credit facilities and private placement notes. If such cash
flow were not sufficient to meet such debt service requirements, the Company
might sell equity securities, refinance its obligations or dispose of one or
more of its properties in order to make such scheduled payments. The Company
may not be able to effect any of such transactions on favorable terms.

  The Company is in the process of negotiating a new credit facility that
would provide for borrowings of up to $2.0 billion. On a pro forma basis,
giving effect as of September 30, 1999, to all pending acquisitions and the
private placement note offering, the Company would have had aggregate
borrowings under its credit facilities of approximately $1.2 billion and no
available cash. Accordingly, the Company must arrange for additional
borrowings or other external funds to complete its pending transactions. One
of the transactions provides for the forfeiture of a $100.0 million deposit if
the Company fails to close. While the Company believes such negotiations will
be successful, the Company does not know what, if any, changes (including
without limitations interest rate increases or other more restrictive
provisions) the lenders may require in connection with such borrowing limit
increase. Upon the execution of a new credit facility, the Company will be
required to recognize an extraordinary loss on extinguishment of debt. If the
new credit facility is executed in the fourth quarter of 1999, such loss would
be approximately $4.2 million, net of a tax benefit of $2.8 million.

  Equity Offerings: During 1999, the Company completed a secondary public
offering and private placement of its securities. See note 5 of the condensed
consolidated financial statements.

  ATC Separation: As of September 30, 1999, the Company continues to be
obligated under the ATC Separation agreement for certain tax indemnification
liabilities to CBS Corporation. See note 2 of the condensed consolidated
financial statements.

                                      20
<PAGE>

  Acquisitions: As of September 30, 1999, the Company was a party to various
agreements relating to the acquisition of assets or businesses from various
third parties. See note 6 of the condensed consolidated financial statements.

Year 2000

  The Company is aware of the issues associated with the year 2000 as it
relates to information systems and is currently working to resolve the
potential impact to the Company's operations. The year 2000 issue results from
the fact that many computer programs use only two digits to identify a year in
the date field. These programs were designed and developed without
consideration of the impact of the upcoming change in century.

  In December 1998, the Company engaged outside consultants to help it conduct
an extensive review and implement a comprehensive plan to reduce the
probability of operational difficulties due to year 2000 issues. The
comprehensive plan consists of the following phases: (1) awareness phase--
identification of the problem and designing a structure to support the year
2000 efforts; (2) definition of critical processes and systems--a process to
identify those activities critical to the Company and focus the efforts of
year 2000 activities; (3) assessment phase--inventory the Company's systems,
software and equipment, assessing whether they are year 2000 compliant,
prioritizing those systems, software and equipment not compliant and
developing action plans for remediation and or replacement of non-complaint
systems, software and equipment; (4) renovation phase--converting, replacing
or retiring non-compliant systems, software and equipment; (5) validation
phase--testing converted or replaced systems; (6) implementation phase--place
converted or replaced systems into operations; and (7) contingency planning
phase--building a backup plan to be used in the event that the renovation plan
cannot be accomplished. This phase will also include business continuity and
disaster recovery planning for possible year 2000 induced failures on core
business processes. The Company's plan considers both its primary information
systems (financial systems software, network software and equipment, personal
computers, etc.) and other technology and software dependent upon embedded
systems (tower equipment, telephone systems, security systems, etc.).

  The Company has completed phases 1 through 5 and is in the process of
completing the remaining two phases for both its primary information systems
and its other systems and equipment with embedded software. These phases are
expected to be completed in the fourth quarter of 1999.

  Through September 30, 1999, the Company has not incurred significant costs
related to developing and implementing its year 2000 comprehensive plan. The
remaining costs necessary to complete full implementation of the plan are
estimated to be between $0.3 million and $0.5 million.

  Although there can be no assurance that the Company will successfully
complete implementation of its year 2000 comprehensive plan, the project is
currently progressing in accordance with timetables established by the
Company. Although failure to complete implementation on a timely basis may
have material adverse financial and operational impacts on the Company, the
Company believes such failure is not reasonably likely. The possible effects
of unsuccessful implementation of the comprehensive plan include the
following: (i) a temporary inability to process transactions, (ii) a temporary
inability to order supplies or materials, (iii) a temporary inability to
timely process orders and billings, and (iv) a temporary inability to deliver
quality products and services to customers.

  The Company's business is dependent upon the systems of various third
parties. With regard to these vendors, the Company is in the process of
assessing their year 2000 readiness based upon communications with each such
vendor. The assessment is expected to be ongoing throughout the fourth quarter
of 1999. The Company believes that a material financial or business risk could
occur if the financial institutions serving the Company or the Company's
utility providers have year 2000 induced failures. The Company understands
that these institutions and providers are cognizant of the year 2000 issues
and are actively working to solve any problems that may arise.

                                      21
<PAGE>

  The Company believes that its most reasonably likely worst case result
relating to year 2000 would be the failure of certain of its systems with
embedded software, or failure of third party systems on which the Company's
systems rely. Failure of systems or equipment with embedded software within
the Company's VVDI segment could result in temporary disruption to that aspect
of the Company's operations. Although there can be no assurance that these
failures would not have an adverse effect on the Company's business, the
Company believes the effect of such failure would not be material to its
business. If the VVDI operations were inoperable for a one week period due to
year 2000 failures, the estimated lost revenue would be approximately $0.6
million.

  Within its rental and management business segment, computer-controlled
devices, such as those found in automatic monitoring and control systems used
for antenna structure lighting, are vulnerable to year 2000 related
malfunctions and may fail, which would create a hazard to air navigation.
Tower owners, such as the Company, are responsible for tower lighting in
compliance with Federal Communications Commission and the Federal Aviation
Administration requirements and the Company intends to take the necessary
steps to address the year 2000 issues; however, the Company may not be
entirely successful.

  Currently there are no contingency plans for the potential problems noted
above with the third party vendors, embedded software and lighting systems;
however, the Company has implemented a contingency planning phase for those or
other matters as part of its year 2000 plan. The contingency planning phase is
estimated to be completed in the later part of the fourth quarter of 1999.

Recent Accounting Pronouncement

  In June 1998, the Financial Accounting Standards Board (FASB) issued
Statement of Financial Accounting Standards (FAS) No. 133, Accounting for
Derivative Instruments and Hedging Activities, as amended in May 1999 by FAS
No. 137. This statement establishes accounting and reporting standards for
derivative instruments. It requires that an entity recognize all derivatives
as either assets or liabilities in the statement of financial position, and
measure those instruments at fair value. The accounting for changes in the
fair value of a derivative (that is, gains and losses) will depend on the
entity's intended use of the derivative and its resulting designation (as
defined in the statement). FAS No. 133, as amended, is effective for all
fiscal quarters of all fiscal years beginning after January 1, 2001. The
Company is currently in the process of evaluating the impact FAS No. 133 will
have on the Company and its consolidated financial statements.

                                      22
<PAGE>

ITEM 3. QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK

  The Company maintains a portion of its cash and cash equivalents in short-
term financial instruments which are subject to interest rate risks. Due to
the relatively short duration of such instruments, fluctuations in interest
rates should not materially affect the Company's financial condition or
results of operations.

  The Company is exposed to market risk from changes in interest rates on
long-term debt obligations that impact the fair value of these obligations.
The Company attempts to reduce these risks by utilizing derivative financial
instruments, namely interest rate caps and swaps, pursuant to Company
policies. All derivative financial instruments are for purposes other than
trading.

  In October 1999, the Company issued the 6.25% and 2.25% Notes and received
total net proceeds of approximately $584.0 million. Of the total proceeds
received, $368.0 million was used to pay off outstanding debt under the
Company's existing credit facility. In paying off such debt, which accrued
interest based on a variable rate, the Company has substantially reduced its
market risk from changes in interest rates as the interest under the 6.25% and
2.25% Notes accrues based on a fixed rate. The Company does, however, continue
to have $483.0 million available to it under the existing credit facility and
is in the process of negotiating a new $2.0 billion credit facility. The
Company may borrow from its existing facility and if implemented, its new
facility at its discretion. Should the Company elect to borrow, it would
subject itself to market risk as described under this Section in the Company's
Annual Report on Form 10-K.

  Except as discussed above, for the three months ended September 30, 1999,
the Company has not incurred any material changes with respect to the interest
rates on long-term debt and interest rate caps and swaps disclosed under this
section in its 1998 Annual Report on Form 10-K and its March 31, 1999 and June
30, 1999 quarterly reports on Form 10-Q. Accordingly, refer to Item 7A in the
Company's Annual Report on Form 10-K for a more detailed discussion.

                                      23
<PAGE>

                          PART II. OTHER INFORMATION

Item 1.--Legal Proceedings.

  The Company periodically becomes involved in various claims and lawsuits
that are incidental to its business. In the opinion of management, after
consultation with counsel, there are no matters currently pending which would,
in the event of adverse outcome, have a material impact on the Company's
consolidated financial position, the results of its operations or liquidity.

Item 2.--Changes in Securities and Use of Proceeds.

  On October 4, 1999, the Company completed a private placement of $300.0
million principal amount of 6.25% Convertible Notes due 2009, issued at 100%
of their face amount, and $425.5 million principal amount of 2.25% Convertible
Notes due 2009, issued at 70.52% of their face amount, to certain
institutional purchasers pursuant to the exemption from registration provided
by section 4(2) of the Securities Act of 1933, as amended. The 6.25% Notes are
convertible to Class A Common Stock at the option of the holder at a
conversion price of $24.40 per share and the 2.25% Notes are convertible to
Class A Common Stock at the option of the holder at a conversion price of
$24.00.

  The net proceeds to the Company from such sale were approximately $584.0
(after deduction of the initial purchaser's discount and estimated offering
expenses). In October 1999, the Company used approximately $368.0 million of
such net proceeds to repay outstanding borrowings under its credit facilities.
The balance was invested in short-term investment grade securities and will be
used to finance acquisitions and construction. None of the expenses paid in
connection with the distribution of the 6.25% Notes or 2.25% Notes in the
offering, and none of the net offering proceeds, were paid directly or
indirectly to directors, officers, or general partners of the Company or their
associates, persons owning 10% or more of any class of the Company's
securities, or affiliates of the Company.

Item 6.--Exhibits and Reports on Form 8-K.

 (a) Exhibits.

  Listed below are the exhibits which are filed as part of this Form 10-Q
(according to the number assigned to them in Item 601 of Regulation S-K). Each
exhibit marked by a (*) is incorporated by reference to the filing of the
Company's Registration Statement on Form S-3 (File No. 333-89345) on October
20, 1999.

<TABLE>
<CAPTION>
 Exhibit No.                Description of Document                       Exhibit File No.
 -----------                -----------------------                       ----------------
 <C>         <S>                                                    <C>
  4.1        Indenture, by and between the Company and The Bank
              of New York as Trustee, for the 6.25% Notes, dated
              as of October 4, 1999, including form of 6.25%
              Note................................................  (*4.1)
  4.2        Indenture by and between the Company and The Bank of
              New York as Trustee, for the 2.25% Notes, dated as
              of October 4, 1999, including the form of 2.25%
              Note................................................  (*4.2)
  4.3        Form of 6.25% Note (included in Exhibit 4.1).........  Filed as part of Exhibit
                                                                    4.1(*)
  4.4        Form of 2.25% Note (included in Exhibit 4.2).........  Filed as part of Exhibit
                                                                    4.2(*)
  4.5        Registration Rights Agreement, by and between the
              Company and the Initial Purchasers named therein,
              dated as of October 4, 1999.........................  (*4.5)
 10.1        Third Amendment to ATS Facility A Loan Agreement,
              dated as of July 9, 1999, by and among American
              Tower, L.P. (formerly known as American Tower
              Systems, L.P.), a Delaware limited partnership
              (ATLP), and American Towers, Inc. (formerly known
              as American Tower Systems (Delaware), Inc.), a
              Delaware corporation (ATI), as borrowers, and
              Toronto Dominion (Texas), Inc. as Administrative
              Agent, and the Banks parties thereto................  Filed herewith as Exhibit
                                                                    10.1

</TABLE>

                                      24
<PAGE>

<TABLE>
<CAPTION>
 Exhibit No.                Description of Document                      Exhibit File No.
 -----------                -----------------------                      ----------------
 <C>         <S>                                                   <C>
 10.2        Fourth Amendment to Facility A Loan Agreement and
              Consent, dated as of September 29, 1999, by and
              among ATLP and ATI, as borrowers, and Toronto
              Dominion (Texas), Inc. as Administrative Agent, and
              the Banks parties thereto........................... Filed herewith as Exhibit
                                                                   10.2

 10.3        Third Amendment to ATS Facility B Loan Agreement,
              dated as of May 27, 1999, by and among ATLP and
              ATI, as borrowers, and Toronto Dominion (Texas),
              Inc. as Administrative Agent, and the Banks parties
              thereto............................................. Filed herewith as Exhibit
                                                                   10.3

 10.4        Fourth Amendment to ATS Facility B Loan Agreement,
              dated as of July 9, 1999, by and among ATLP and
              ATI, as borrowers, and Toronto Dominion (Texas),
              Inc. as Administrative Agent, and the Banks parties
              thereto............................................. Filed herewith as Exhibit
                                                                   10.4

 10.5        Fifth Amendment to Facility B Loan Agreement and
              Consent, dated as of September 29, 1999, by and
              among ATLP and ATI, as borrowers, and Toronto
              Dominion (Texas), Inc. as Administrative Agent, and
              the Banks parties thereto........................... Filed herewith as Exhibit
                                                                   10.5

 10.6        First Amendment to Parent Loan Agreement, dated as
              of July 9, 1999, by and among the Company, as
              borrower, and Toronto Dominion (Texas), Inc. as
              Administrative Agent, and the Banks parties
              thereto............................................. Filed herewith as Exhibit
                                                                   10.6

 10.7        Agreement to Sublease, dated as of August 6, 1999,
              by and between Airtouch Communications, Inc., the
              other parties named therein as sublessors, the
              Company and ATLP.................................... Incorporated by reference to
                                                                   Exhibit 10.1 from the
                                                                   Company's Quarterly Report
                                                                   on form 10-Q for the quarter
                                                                   ended June 30, 1999

 10.8        Stock Purchase Agreement, dated as of August 11,
              1999, between ATC Teleports, Inc., ICG Holdings,
              Inc. and ICG Satellite Services..................... Incorporated by reference to
                                                                   Exhibit 10.2 from the
                                                                   Company's Quarterly Report
                                                                   on Form 10-Q for the quarter
                                                                   ended June 30, 1999

 10.9        Purchase and Sale Agreement, dated as of September
              10, 1999, by and among the Company and AT&T Corp.,
              a New York corporation.............................. Incorporated by reference to
                                                                   Exhibit 10.1 from the
                                                                   Company's Current Report on
                                                                   Form 8-K dated September 17,
                                                                   1999

 27          Financial Data Schedule.............................. Filed herewith as Exhibit 27
</TABLE>

 (b) Reports on Form 8-K.

  1. Form 8-K (Items 5 and 7) filed on July 16, 1999.
  2. Form 8-K (Items 5 and 7) filed on September 17, 1999.
  3. Form 8-K (Items 5 and 7) filed on September 17, 1999.
  4. Form 8-K (Items 5 and 7) filed on September 21, 1999.

                                       25
<PAGE>

                                  SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the
Registrant has duly caused this report to be signed on its behalf by the
undersigned, thereunto duly authorized.

                                          American Tower Corporation

                                          By:      /s/ Joseph L. Winn
Date: November 15, 1999                      ---------------------------------
      ------------------                     Joseph L. Winn
                                             Treasurer & Chief Financial Officer
                                             (Duly Authorized Officer)

                                          By:      /s/ Justin D. Benincasa
Date: November 15, 1999                      ---------------------------------
      -----------------                      Justin D. Benincasa
                                             Vice President & Corporate
                                             Controller
                                             (Duly Authorized Officer)

                                      26

<PAGE>

                                                                    EXHIBIT 10.1
                                                                    ------------

                               THIRD AMENDMENT TO
                         ATS FACILITY A LOAN AGREEMENT


     THIS THIRD AMENDMENT TO ATS FACILITY A LOAN AGREEMENT (this "Amendment"),
                                                                  ---------
dated as of the 9th day of July, 1999 (the "Amendment Date"), by and among
                                            --------------
AMERICAN TOWER, L.P., a Delaware limited partnership, and AMERICAN TOWERS, INC.,
a Delaware corporation (collectively, the "Borrower"), the FINANCIAL
                                           --------
INSTITUTIONS SIGNATORY HERETO and TORONTO DOMINION (TEXAS), INC., as
administrative agent (the "Administrative Agent") for the Banks (as defined in
                           --------------------
the Loan Agreement defined below);


                              W I T N E S S E T H:
                              -------------------


     WHEREAS, the Borrower, the Banks and the Administrative Agent are parties
to that certain ATS Facility A Loan Agreement dated as of June 16, 1998, as
amended by that certain First Amendment to ATS Facility A Loan Agreement dated
as of October 30, 1998 and that certain Second Amendment and Waiver to ATS
Facility A Loan Agreement dated as of February 8, 1999 (as amended, modified,
supplemented and restated from time to time, the "Loan Agreement"); and
                                                  --------------

     WHEREAS, the Borrower has requested, and the Banks have agreed, on the
terms and subject to the conditions set forth herein, to add letter of credit
availability, as a sublimit, under the Revolving Loan Commitment and to make
certain other amendments to the Loan Agreement, in each case, as provided
herein;

     NOW, THEREFORE, in consideration of the premises set forth above, the
covenants and agreements hereinafter set forth, and other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged, the
parties hereto agree that all capitalized terms used herein shall have the
meanings ascribed thereto in the Loan Agreement, and further agree as follows:

     1.   Amendments to Article 1.
          -----------------------

     (a)  Article 1 of the Loan Agreement, Definitions, is hereby amended by
                                           -----------
adding the following definitions of "Available Letter of Credit Commitment,"
                                     -------------------------------------
"Available Revolving Loan Commitment," "Broker/Dealer," "Commercial Letter of
 -----------------------------------    -------------    --------------------
Credit," "communications site," "Issuing Bank," "Letter of Credit Obligations,"
- ------    -------------------    ------------    ----------------------------
"Letter of Credit Reserve Account," "Letters of Credit," "Request for Issuance
 --------------------------------    -----------------    --------------------
of Letter of Credit" and "Standby Letter of Credit" thereto in appropriate
- -------------------       ------------------------
alphabetical order:
<PAGE>

     "'Available Letter of Credit Commitment' shall mean, at any time, the
       -------------------------------------
lesser of (a) (i) $35,000,000, minus (ii) all Letter of Credit Obligations then
                               -----
outstanding, and (b) (i) the Revolving Loan Commitment, minus (ii) the Revolving
                                                        -----
Loans then outstanding."

     "'Available Revolving Loan Commitment' shall mean, as of any date, (a) the
       -----------------------------------
several obligations of the Banks to advance up to $400,000,000 to the Borrower
pursuant to the terms hereof, minus (b) the aggregate amount of all Letter of
Credit Obligations then outstanding."

     "'Broker/Dealer' shall mean, with respect to any Investment or Acquisition
       -------------
permitted under Section 7.6(a) hereof, (a) any broker/dealer (acting as
principal) registered as a broker or a dealer under Section 15 of the Exchange
Act, the unsecured short-term debt obligations of which are rated "P-1" by
Moody's Investors Service, Inc. and at least "A-1" by Standard and Poor's
Ratings Group, a division of The McGraw-Hill Companies, Inc., at the time of
entering into such Investment or Acquisition or (b) an unrated, broker/dealer,
acting as principal, that is a wholly-owned Subsidiary of a non-bank or bank
holding company, the unsecured short-term debt obligations of which are rated
"P-1" by Moody's Investors Service, Inc. and at least "A-1" by Standard and
Poor's Ratings Group, a division of The McGraw-Hill Companies, Inc., at the time
of entering into such Investment or Acquisition."

     "'Commercial Letter of Credit' shall mean a documentary letter of credit
       ---------------------------
issued in respect of the purchase of goods or services by the Borrower or its
Restricted Subsidiaries by the Issuing Bank in accordance with the terms
hereof."

     "'communications site' shall mean (a) any undeveloped real property and (b)
       -------------------
communication towers which have no bona fide customers on the date of
acquisition thereof."

     "'Issuing Bank' shall mean The Toronto-Dominion Bank, New York Branch, as
       ------------
issuer of the Letters of Credit, and its successors and assigns hereunder."

     "'Letter of Credit Obligations' shall mean, at any time, the sum of (a) an
       ----------------------------
amount equal to the aggregate undrawn and unexpired amount (including the amount
to which any such Letter of Credit can be reinstated pursuant to the terms
hereof) of the then outstanding Letters of Credit and (b) an amount equal to the
aggregate drawn, but unreimbursed drawings on any Letters of Credit."

     "'Letter of Credit Reserve Account' shall mean any account maintained by
       --------------------------------
the Administrative Agent for the benefit of the Issuing Bank, the proceeds of
which shall be applied as provided in Section 8.2(g) hereof."

                                      -2-
<PAGE>

     "'Letters of Credit' shall mean either Standby Letters of Credit or
       -----------------
Commercial Letters of Credit issued by the Issuing Bank on behalf of the
Borrower or its Restricted Subsidiaries from time to time in accordance with the
terms hereof."

     "'Request for Issuance of Letter of Credit' shall mean any certificate
       ----------------------------------------
signed by an Authorized Signatory of the Borrower requesting that the Issuing
Bank issue a Letter of Credit hereunder, which certificate shall be in
substantially the form of Exhibit U attached hereto and shall, among other
things, specify (a) that the requested Letter of Credit is either a Commercial
Letter of Credit or a Standby Letter of Credit, (b) the stated amount of the
Letter of Credit, (c) the effective date for the issuance of the Letter of
Credit (which shall be a Business Day), (d) the date on which the Letter of
Credit is to expire (which shall be a Business Day), (e) the Person for whose
benefit such Letter of Credit is to be issued, and (f) other relevant terms of
such Letter of Credit."

     "'Standby Letter of Credit' shall mean a letter of credit issued to support
       ------------------------
obligations of the Borrower or its Restricted Subsidiaries incurred in the
ordinary course of business, and which is not a Commercial Letter of Credit."

     (b)  Article 1 of the Loan Agreement, Definitions, is hereby amended by
                                          -----------
deleting the definitions of "Fixed Charges Coverage Ratio," "Loan Documents,"
                             ----------------------------    --------------
"Obligations" and "Subsidiary" in their entirety and by substituting the
 -----------       ----------
following in lieu thereof in appropriate alphabetical order:

          "'Fixed Charges Coverage Ratio' shall mean, as of any calculation
            ----------------------------
     date, the ratio of (a) the sum of (i) Annualized Operating Cash Flow as of
     the most recently completed fiscal quarter, plus (ii) the sum of (A) the
     amount of unused Commitments as of such date under this Agreement and the
     ATS Facility B Loan Agreement which could be borrowed on such date in
     compliance with Section 7.8 hereof, plus, (B) to the extent then reflected
                                         ----
     as net cash on the balance sheet of either Borrower, the net cash proceeds
     of any equity issued, directly or indirectly, by either Borrower and
     received by either Borrower from the Parent (after deducting any portion
     thereof applied to the Loans or the Facility B Loans) to (b) Fixed
     Charges."

          "'Loan Documents' shall mean this Agreement, the Notes, the Security
            --------------
     Agreements, the Borrowers' Guarantees, the Stock Pledge Agreement, all
     Subsidiary Pledge Agreements, all Subsidiary Security Agreements, all
     Subsidiary Guaranties, all Assignments of Intercompany Notes, all
     Subordination Agreements, the Parent Guaranty, the Parent Pledge Agreement,
     the Assignment of Limited Partner Interests, the Assignment of General
     Partner Interests, all fee letters, all Requests for Advance, all Letters
     of Credit, all Interest Hedge Agreements between either Borrower, on the
     one hand, and the Administrative Agent and the Banks, or any of them, on
     the other hand, and all other documents and agreements executed or
     delivered by either Borrower or any of the Restricted

                                      -3-
<PAGE>

     Subsidiaries or the Parent in connection with or contemplated by this
     Agreement; provided, however, that Loan Documents shall exclude, except as
                --------  -------
     otherwise specifically provided herein, the "Loan Documents" under the
     Parent Loan Agreement."

          "'Obligations' shall mean all payment and performance obligations of
            -----------
     every kind, nature and description of the Borrowers, the Restricted
     Subsidiaries, and any other obligors to the Banks, the Issuing Bank or the
     Administrative Agent, or any of them, under this Agreement and the other
     Loan Documents (including, without limitation, any interest, fees and other
     charges on the Loans or otherwise under the Loan Documents that would
     accrue but for the filing of a bankruptcy action with respect to either
     Borrower, whether or not such claim is allowed in such bankruptcy action,
     Obligations to the Banks pursuant to Section 5.12 hereof and the Letter of
     Credit Obligations), as they may be amended from time to time, or as a
     result of making the Loans, whether such obligations are direct or
     indirect, absolute or contingent, due or not due, contractual or tortious,
     liquidated or unliquidated, arising by operation of law or otherwise, now
     existing or hereafter arising."

          "'Subsidiary' shall mean, as applied to any Person, (a) any
            ----------
     corporation of which no less than fifty percent (50%) of the outstanding
     stock (other than directors' qualifying shares) having ordinary voting
     power to elect a majority of its board of directors, regardless of the
     existence at the time of a right of the holders of any class or classes of
     securities of such corporation to exercise such voting power by reason of
     the happening of any contingency, or any partnership of which no less than
     fifty percent (50%) of the outstanding partnership interests, is at the
     time owned directly or indirectly by such Person, or by one or more
     Subsidiaries of such Person, or by such Person and one or more Subsidiaries
     of such Person; provided, however, that if such Person and/or such Person's
                     --------  -------
     Subsidiaries directly or indirectly own no more than fifty percent (50%) of
     such Subsidiary's ownership interests, then such Subsidiary's operating or
     governing documents must require (i) such Subsidiary's net cash after the
     establishment of reserves be distributed to its equity holders no less
     frequently than quarterly and (ii) the consent of such Person and/or such
     Person's Subsidiaries to amend or otherwise modify the provisions of such
     operating or governing documents requiring such distributions, or (b) any
     other entity which is directly or indirectly controlled or capable of being
     controlled by such Person, or by one or more Subsidiaries of such Person,
     or by such Person and one or more Subsidiaries of such Person."

                                      -4-
<PAGE>

     2.   Amendments to Article 2.
          -----------------------

     (a)  Amendments to Section 2.1.
          -------------------------

          (i) Section 2.1 of the Loan Agreement, The Loans, is hereby amended by
     deleting subsection (a) thereof in its entirety and by substituting the
     following in lieu thereof:

              "(a) Revolving Loan Commitment. The Banks agree, severally, in
                   -------------------------
          accordance with their respective Commitment Ratios, and not jointly,
          upon the terms and subject to the conditions of this Agreement, to
          lend and relend to the Borrowers from time to time, amounts which do
          not exceed, in the aggregate, at any one time outstanding the amount
          of the Available Revolving Loan Commitment as in effect from time to
          time. Subject to the terms and conditions hereof, Advances under the
          Revolving Loan Commitment may be repaid and reborrowed from time to
          time on a revolving basis. The Borrowers hereby agree that all amounts
          advanced under the Revolving Loan Commitment shall be joint and
          several obligations of the Borrowers."

          (ii) Section 2.1 of the Loan Agreement, The Loans, is hereby further
                                                  ---------
     amended by adding the following new subsection (c) thereto:

              "(c) The Letters of Credit. Subject to the terms and conditions of
                   ---------------------
          this Agreement, the Issuing Bank agrees to issue Letters of Credit for
          the account of the Borrower (for itself and on behalf of its
          Restricted Subsidiaries) pursuant to Section 2.14 hereof in an
          aggregate amount not to exceed the Available Letter of Credit
          Commitment determined immediately prior to giving effect to the
          issuance thereof."

          (b) Amendment to Section 2.4. Section 2.4 of the Loan Agreement,
              ------------------------
Commitment Fees, is hereby amended by redesignating such Section as "Fees",
- ---------------                                                      ----
designating the existing Section as "(a)", and adding the following new
subsection (b) thereto immediately following Section 2.4(a):

              "(b) Letter of Credit Fees. (i) The Borrower shall pay to the
                   ---------------------
          Issuing Bank a fee on the stated amount (reduced by the amount of any
          draws) of any outstanding Letters of Credit from the date of issuance
          through the expiration date of each such Letter of Credit at a rate of
          one eighth of one percent (0.125%) per annum, which fee shall be
          computed on the basis of a year of 365/366 days for the actual number
          of days elapsed, and shall be payable quarterly in arrears on the last
          day of each calendar quarter commencing on September 30, 1999.

                   (ii) The Borrower shall also pay to the Administrative Agent
          on behalf of the Banks in accordance with their respective Commitment
          Ratios, a fee

                                      -5-
<PAGE>

          on the stated amount (reduced by the amount of any draws) of any
          outstanding Letters of Credit for each day from the date of issuance
          thereof through the expiration date for each such Letter of Credit at
          a rate equal to the Applicable Margin for LIBOR Advances under the
          Revolving Loan Commitment. Such Letter of Credit Fee shall be computed
          on the basis of a year of 365/366 days for the actual number of days
          elapsed, shall be payable quarterly in arrears for each quarter on the
          last day of each calendar quarter commencing on September 30, 1999.
          The Letter of Credit Fee set forth in this Section 2.4 (b) (ii) shall
          be subject to increase and decrease on the dates and in the amounts
          set forth in Section 2.3(f) hereof in the same manner as the
          adjustment of the Applicable Margin with respect to LIBOR Advances
          upon satisfaction of the requirements set forth in Section 2.3(f)
          hereof."

          (c) Amendment to Section 2.7. Section 2.7(b) of the Loan Agreement,
              ------------------------
Prepayments Repayments: Repayments, is hereby amended by deleting subsection
- ----------------------------------
(ii) thereof in its entirety and substituting the following in lieu thereof:

              "(ii) Revolving Loans and Letter of Credit Obligations in Excess
                    ----------------------------------------------------------
          of Revolving Loan Commitment. If, at any time, the amount of the
          ----------------------------
          Revolving Loans and Letter of Credit Obligations shall exceed the
          Revolving Loan Commitment, the Borrowers shall, on such date and
          subject to Section 2.10 hereof, make a repayment of the principal
          amount of the Revolving Loans in an amount equal to such excess,
          together with any accrued interest and fees with respect thereto."

          (d) Article 2 of the Loan Agreement, Loans, is hereby amended by
adding the following new Section 2.14, Letters of Credit, thereto:
                                       -----------------

              "Section 2.14  Letters of Credit.
                             -----------------

                  (a) Subject to the terms and conditions hereof, the Issuing
          Bank, on behalf of the Banks, and in reliance on the agreements of the
          Banks set forth in subsection (d) below, hereby agrees to issue one or
          more Letters of Credit up to an aggregate face amount equal to the
          Available Letter of Credit Commitment determined immediately prior to
          giving effect to the issuance thereof; provided, however, that the
                                                 --------  -------
          Issuing Bank shall not issue any Letter of Credit unless the
          conditions precedent to the issuance thereof set forth in Section 3.3
          hereof have been satisfied, and shall have no obligation to issue any
          Letter of Credit if any Default then exists or would be caused thereby
          or if, after giving effect to such issuance, the Available Revolving
          Loan Commitment minus the Revolving Loans then outstanding would be
                          -----
          less than zero; and provided further, however, that at no time shall
                              -------- -------  -------
          the total Letter of Credit Obligations outstanding hereunder exceed
          $35,000,000. Each Letter of Credit shall (1) be denominated in United
          States dollars, and (2) expire no later than the earlier to occur of
          (A) the Maturity Date, and (B) 360 days after its date of issuance
          (but may contain provisions for

                                      -6-
<PAGE>

          automatic renewal provided that no Default or Event of Default exists
          on the renewal date or would be caused by such renewal). Each Letter
          of Credit shall be subject to the Uniform Customs and Practice for
          Documentary Credits (1993 Revision), International Chamber of Commerce
          Publication No. 500 and, to the extent not inconsistent therewith, the
          laws of the State of New York. The Issuing Bank shall not at any time
          be obligated to issue, or cause to be issued, any Letter of Credit if
          such issuance would conflict with, or cause the Issuing Bank to exceed
          any limits imposed by, any Applicable Law. If a Letter of Credit
          provides that it is automatically renewable unless notice is given by
          the Issuing Bank that it will not be renewed, the Issuing Bank shall
          not be bound to give a notice of non-renewal unless directed to do so
          by the Majority Banks at least sixty-five (65) days prior to the then
          scheduled expiration date of such Letter of Credit.

                   (b) Either Borrower may from time to time request and be
          provided by the Issuing Bank the issuance of Letters of Credit. The
          Borrower shall execute and deliver to the Administrative Agent and the
          Issuing Bank a Request for Issuance of Letter of Credit for each
          Letter of Credit to be issued by the Issuing Bank, not later than
          12:00 noon (New York, New York time) on the fifth (5th) Business Day
          preceding the date on which the requested Letter of Credit is to be
          issued, or such shorter notice as may be acceptable to the Issuing
          Bank and the Administrative Agent. Upon receipt of any such Request
          for Issuance of Letter of Credit, subject to satisfaction of all
          conditions precedent thereto as set forth in Section 3.3 hereof, the
          Issuing Bank shall process such Request for Issuance of Letter of
          Credit and the certificates, documents and other papers and
          information delivered to it in connection therewith in accordance with
          its customary procedures and shall promptly issue the Letter of Credit
          requested thereby. The Issuing Bank shall furnish a copy of such
          Letter of Credit to the Borrower and the Administrative Agent
          following the issuance thereof. The Borrower shall pay or reimburse
          the Issuing Bank for normal and customary costs and expenses incurred
          by the Issuing Bank in issuing, effecting payment under, amending or
          otherwise administering the Letters of Credit.

                   (c) At such time as the Administrative Agent shall be
          notified by the Issuing Bank that the beneficiary under any Letter of
          Credit has drawn on the same, the Administrative Agent shall promptly
          notify the Borrower and each Bank, by telephone or telecopy, of the
          amount of the draw and, in the case of each Bank, such Bank's portion
          of such draw amount as calculated in accordance with its Revolving
          Loan Commitment Ratio.

                   (d) The Borrower hereby agrees to immediately reimburse the
          Issuing Bank for amounts paid by the Issuing Bank in respect of draws
          under a Letter of Credit issued at the Borrower's request. In order to
          facilitate such repayment, the Borrower hereby irrevocably requests
          the Banks having a Revolving Loan Commitment, and such Banks hereby
          severally agree, on the terms and conditions

                                      -7-
<PAGE>

          of this Agreement (other than as provided in Article 2 hereof with
          respect to the amounts of, the timing of requests for, and the
          repayment of Advances hereunder and in Article 3 hereof with respect
          to conditions precedent to Advances hereunder), with respect to any
          drawing under a Letter of Credit prior to the occurrence of an event
          described in clauses (f) or (g) of Section 8.1 hereof, to make an
          Advance (which Advance may be a LIBOR Advance if the Borrower so
          requests in a timely manner or may be converted to a LIBOR Advance as
          provided in the Loan Agreement) to the Borrower on each day on which a
          draw is made under any Letter of Credit and in the amount of such
          draw, and to pay the proceeds of such Advance directly to the Issuing
          Bank to reimburse the Issuing Bank for the amount paid by it upon such
          draw. Each Bank having a Revolving Loan Commitment shall pay its share
          of such Advance by paying its portion of such Advance to the
          Administrative Agent in accordance with Section 2.2(e) hereof and its
          Revolving Loan Commitment Ratio, without reduction for any set-off or
          counterclaim of any nature whatsoever and regardless of whether any
          Default or Event of Default (other than with respect to an event
          described in clauses (f) or (g) of Section 8.1 hereof) then exists or
          would be caused thereby. If at any time that any Letters of Credit are
          outstanding, any of the events described in clauses (f) or (g) of
          Section 8.1 hereof shall have occurred and be continuing, then each
          Bank having a Revolving Loan Commitment shall, automatically upon the
          occurrence of any such event and without any action on the part of the
          Issuing Bank, the Borrower, the Administrative Agent or such Banks, be
          deemed to have purchased an undivided participation in the face amount
          of all Letters of Credit then outstanding in an amount equal to such
          Bank's Revolving Loan Commitment Ratio, and each Bank having a
          Revolving Loan Commitment shall, notwithstanding such Event of
          Default, upon a drawing under any Letter of Credit, immediately pay to
          the Administrative Agent for the account of the Issuing Bank, in
          immediately available funds, the amount of such Bank's participation
          (and the Issuing Bank shall deliver to such Bank a loan participation
          certificate dated the date of the occurrence of such event and in the
          amount of such Bank's Revolving Loan Commitment Ratio). The
          disbursement of funds in connection with a draw under a Letter of
          Credit pursuant to this Section 2.14(d) shall be subject to the terms
          and conditions of Section 2.2(e) hereof. The obligation of each Bank
          having a Revolving Loan Commitment to make payments to the
          Administrative Agent, for the account of the Issuing Bank, in
          accordance with this Section 2.14 shall be absolute and unconditional
          and no such Bank shall be relieved of its obligations to make such
          payments by reason of noncompliance by any other Person with the terms
          of the Letter of Credit or for any other reason. The Administrative
          Agent shall promptly remit to the Issuing Bank the amounts so received
          from the other Banks. Any overdue amounts payable by the Banks having
          a Revolving Loan Commitment to the Issuing Bank in respect of a draw
          under any Letter of Credit shall bear interest, payable on demand, at
          the rate on overnight federal funds transactions with members of the

                                      -8-
<PAGE>

          Federal Reserve System arranged by federal funds brokers, as published
          for such day by the Federal Reserve Bank of New York.

                   (e) The Borrower agrees that any action taken or omitted to
          be taken by the Issuing Bank in connection with any Letter of Credit,
          except for such actions or omissions as shall constitute gross
          negligence or willful misconduct on the part of the Issuing Bank,
          shall be binding on the Borrower as between the Borrower and the
          Issuing Bank, and shall not result in any liability of the Issuing
          Bank to the Borrower. The obligation of the Borrower to reimburse the
          Banks for Advances made to reimburse the Issuing Bank for draws under
          the Letter of Credit shall be absolute, unconditional and irrevocable,
          and shall be paid strictly in accordance with the terms of this
          Agreement under all circumstances whatsoever, including, without
          limitation, the following circumstances:

                   (i) Any lack of validity or enforceability of any Loan
          Document;

                   (ii) Any amendment or waiver of or consent to any departure
          from any or all of the Loan Documents;

                   (iii) Any improper use which may be made of any Letter of
          Credit or any improper acts or omissions of any beneficiary or
          transferee of any Letter of Credit in connection therewith;

                   (iv) The existence of any claim, set-off, defense or any
          right which the Borrower may have at any time against any beneficiary
          or any transferee of any Letter of Credit (or Persons for whom any
          such beneficiary or any such transferee may be acting) or any Bank
          (other than the defense of payment to such Bank in accordance with the
          terms of this Agreement) or any other Person, whether in connection
          with any Letter of Credit, any transaction contemplated by any Letter
          of Credit, this Agreement, any other Loan Document, or any unrelated
          transaction;

                   (v) Any statement or any other documents presented under any
          Letter of Credit proving to be insufficient, forged, fraudulent or
          invalid in any respect or any statement therein being untrue or
          inaccurate in any respect whatsoever, provided that such payment shall
          not have constituted gross negligence or willful misconduct of the
          Issuing Bank;

                   (vi) The insolvency of any Person issuing any documents in
          connection with any Letter of Credit;

                   (vii) Any breach of any agreement between the Borrower and
          any beneficiary or transferee of any Letter of Credit, provided that
                                                                 --------
          the same shall not

                                      -9-
<PAGE>

          have resulted from the gross negligence or willful misconduct of the
          Issuing Bank;

                   (viii) Any irregularity in the transaction with respect to
          which any Letter of Credit is issued, including any fraud by the
          beneficiary or any transferee of such Letter of Credit, but excluding
          any irregularity resulting from the gross negligence or willful
          misconduct of the Issuing Bank;

                   (ix) Any errors, omissions, interruptions or delays in
          transmission or delivery of any messages, by mail, cable, telegraph,
          wireless or otherwise, whether or not they are in code, provided that
          the same shall not be the result of the gross negligence or willful
          misconduct of the Issuing Bank;

                   (x) Any act, error, neglect or default, omission, insolvency
          or failure of business of any of the correspondents of the Issuing
          Bank, provided that the same shall not have constituted the gross
          negligence or willful misconduct of the Issuing Bank;

                   (xi) Any other circumstances arising from causes beyond the
          control of the Issuing Bank;

                   (xii)  Payment by the Issuing Bank under any Letter of Credit
          against presentation of a sight draft or a certificate which does not
          comply with the terms of such Letter of Credit, provided that such
          payment shall not have constituted gross negligence or willful
          misconduct of the Issuing Bank; and

                   (xiii) Any other circumstance or happening whatsoever,
          whether or not similar to any of the foregoing, provided that such
          other circumstances or happenings shall not have been the result of
          gross negligence or willful misconduct of the Issuing Bank or any
          Bank.

                   (f) If any change in Applicable Law, any change in the
          interpretation or administration thereof, or any change in compliance
          with Applicable Law by the Issuing Bank or any Bank as a result of any
          official request or directive of any governmental authority, central
          bank or comparable agency (whether or not having the force of law)
          shall (i) impose, modify or deem applicable any reserve (including,
          without limitation, any imposed by the Board of Governors of the
          Federal Reserve System), special deposit, capital adequacy, assessment
          or other requirements or conditions against Letters of Credit issued
          by the Issuing Bank or against participations by any other Bank in the
          Letters of Credit or (ii) impose on the Issuing Bank or any other Bank
          any other condition regarding any Letter of Credit or any
          participation therein, and the result of any of the foregoing in the
          reasonable determination of the Issuing Bank or such Bank, as the case
          may be, is to increase the cost to the Issuing Bank or such Bank of
          issuing or maintaining

                                      -10-
<PAGE>

          any Letter of Credit or purchasing or maintaining any participation
          therein, as the case may be, by an amount (which amount shall be
          reasonably determined) deemed by the Issuing Bank or such Bank to be
          material, and the designation of a different lending office will not
          avoid the need for additional compensation, then, on request by the
          Issuing Bank or such Bank, the Borrower shall pay, within ten (10)
          days after demand, the Issuing Bank or such Bank, as the case may be,
          such additional amount or amounts as the Issuing Bank or such Bank, as
          the case may be, so determines will compensate it for such increased
          costs. A certificate of the Issuing Bank or such Bank setting forth
          the amount, and in reasonable detail the basis for the Issuing Bank or
          such Bank's determination of such amount, to be paid to the Issuing
          Bank or such Bank by the Borrower as a result of any event referred to
          in this paragraph shall, absent manifest error, be conclusive.

                   (g) Each Bank having a Revolving Loan Commitment shall be
          responsible for its pro rata share (based on such Bank's Revolving
          Loan Commitment Ratio) of any and all reasonable out-of-pocket costs,
          expenses (including reasonable legal fees) and disbursements which may
          be incurred or made by the Issuing Bank in connection with the
          collection of any amounts due under, the administration of, or the
          presentation or enforcement of any rights conferred by any Letter of
          Credit, the Borrower's or any guarantor's obligations to reimburse or
          otherwise. In the event the Borrower shall fail to pay such expenses
          of the Issuing Bank within ten (10) days after demand for payment by
          the Issuing Bank, each Bank having a Revolving Loan Commitment shall
          thereupon pay to the Issuing Bank its pro rata share (based on such
          Bank's Revolving Loan Commitment Ratio) of such expenses within five
          (5) days from the date of the Issuing Bank's notice to the Banks
          having a Revolving Loan Commitment of the Borrower's failure to pay;
          provided, however, that if the Borrower or any guarantor shall
          --------  -------
          thereafter pay such expense, the Issuing Bank will repay to each Bank
          having a Revolving Loan Commitment Ratio the amounts received from
          such Bank hereunder.

                   (h) The Borrower agrees that each Advance by the Banks having
          a Revolving Loan Commitment to reimburse the Issuing Bank for draws
          under any Letter of Credit, shall, for all purposes hereunder, be
          deemed to be an Advance under the Revolving Loan Commitment to the
          Borrower and shall be payable and bear interest in accordance with all
          other Loans to the Borrower.

                   (i) The Borrower will indemnify and hold harmless the
          Administrative Agent, the Issuing Bank and each other Bank and each of
          their respective employees, representatives, officers and directors
          from and against any and all claims, liabilities, obligations, losses
          (other than loss of profits), damages, penalties, actions, judgments,
          suits, costs, expenses or disbursements of any kind or nature
          whatsoever (including reasonable attorneys' fees, but excluding taxes)
          which may be imposed on, incurred by or asserted against the
          Administrative

                                      -11-
<PAGE>

          Agent, the Issuing Bank or any such other Bank in any way relating to
          or arising out of the issuance of a Letter of Credit, except that the
          Borrower shall not be liable to the Administrative Agent, the Issuing
          Bank or any such Bank for any portion of such claims, liabilities,
          obligations, losses, damages, penalties, actions, judgments, suits,
          costs, expenses, or disbursements resulting from the gross negligence
          or willful misconduct of the Administrative Agent, the Issuing Bank or
          such Bank, as the case may be, as determined by a non-appealable
          judicial order. This Section 2.14(i) shall survive termination of this
          Agreement."

     3. Amendment to Article 3. Article 3 of the Loan Agreement, Conditions
        ----------------------                                   ----------
Precedent, is hereby amended by adding the following new Section 3.3 thereto:
- ---------


        "Section 3.3 Conditions Precedent to Issuance of Letters of Credit. The
                     -----------------------------------------------------
     obligation of the Issuing Bank to issue each Letter of Credit hereunder is
     subject to the fulfillment of each of the following conditions immediately
     prior to or contemporaneously with such issuance:

        (a)  All of the representations and warranties of the Borrower under
     this Agreement, which, in accordance with Section 4.2 hereof, are made at
     and as of the time of an Advance, shall be true and correct, both before
     and after giving effect to the issuance of such Letter of Credit;

        (b)  The incumbency of the Authorized Signatories shall be as stated in
     the applicable certificate of incumbency contained in the certificate of
     the Borrower delivered pursuant to Section 3.1(a) hereof or as subsequently
     modified and reflected in a certificate of incumbency delivered to the
     Administrative Agent and the Banks having a Revolving Loan Commitment;

        (c)  There shall not exist, on the date of the issuance of such Letter
     of Credit and after giving effect thereto, a Default or an Event of Default
     hereunder and, the Administrative Agent shall have received a Request for
     Issuance of a Letter of Credit so certifying; and

        (d)  The Administrative Agent, the Issuing Bank and each of the Banks
     having a Revolving Loan Commitment shall have received all such other
     certificates, reports, statements, opinions of counsel (if such Letter of
     Credit is in connection with an Acquisition) or other documents as any of
     them may reasonably request."

     4. Amendments to Article 7.
        -----------------------

     (a)  Amendments to Section 7.6. Section 7.6 of the Loan Agreement,
          -------------------------
Investments and Acquisitions, is hereby amended by deleting subsections (a), (b)
- ----------------------------
and (c) thereof in their entirety and by substituting the following in lieu
thereof:

                                      -12-
<PAGE>

                   "(a) directly or through a brokerage account or investment
          adviser (i) purchase marketable, direct obligations of the United
          States of America, its agencies and instrumentalities maturing within
          three hundred sixty-five (365) days of the date of purchase, (ii)
          purchase commercial paper and other short-term obligations and
          business savings accounts issued by corporations, each of which shall
          have a combined net worth of at least $100,000,000 and each of which
          conducts a substantial part of its business in the United States of
          America, maturing within two hundred seventy (270) days from the date
          of the original issue thereof, and whose issuer is, at the time of
          purchase, rated "P-2" or better by Moody's Investors Service, Inc. or
          "A-2" or better by Standard and Poor's Ratings Group, a division of
          The McGraw-Hill Companies, Inc., (iii) purchase repurchase agreements,
          bankers' acceptances, and domestic and Eurodollar certificates of
          deposit maturing within three hundred sixty-five (365) days of the
          date of purchase which are issued by, or time deposits maintained
          with, (A) a United States national or state bank (or any domestic
          branch of a foreign bank) subject to supervision and examination by
          federal or state banking or depository institution authorities and
          having capital, surplus and undivided profits totaling more than
          $100,000,000 and rated "A" or better by Moody's Investors Service,
          Inc. or Standard and Poor's Ratings Group, a division of The McGraw-
          Hill Companies, Inc., or (B) a Broker/Dealer, and (iv) invest in money
          market funds having a rating from Moody's Investors Service, Inc. and
          Standard and Poor's Ratings Group, a division of The McGraw-Hill
          Companies, Inc. in the highest investment category granted thereby;

                   (b) so long as no Default then exists or would be caused
          thereby, establish Unrestricted Subsidiaries and make Investments in
          such Unrestricted Subsidiaries of up to, in the aggregate, at any
          time, the sum of (i) $60,000,000 with loans borrowed under this
          Agreement or the ATS Facility B Loan Agreement, and (ii) equity
          proceeds not used to pay the Separation Obligations or to make
          Investments permitted under Sections 7.6(c) and (d) hereof;

                   (c) so long as no Default then exists or would be caused
          thereby, and subject to compliance with Section 5.13 hereof, make
          Acquisitions; provided, however, that Acquisitions of communications
                        --------  -------
          sites, tower management businesses and other services businesses, such
          as construction and teleport businesses, shall not exceed, in the
          aggregate, at any time, the sum of (i) $50,000,000 and (ii) equity
          proceeds not used to pay the Separation Obligations after the
          Agreement Date or to make Investments permitted under Sections 7.6(b)
          and (d) hereof;"

          (b) Amendments to Sections 7.8, 7.9, 7.11 and 7.12. Sections 7.8, 7.9,
              ----------------------------------------------
7.11 and 7.12 of the Loan Agreement are hereby amended by inserting the
following phrase immediately

                                      -13-
<PAGE>

following "and (b)"where it appears in such Sections: "at the time of the
issuance of any Letter of Credit (after giving effect to such Letter of Credit),
and (c)".

     5. Amendments to Section 8.2.  Section 8.2 of the Loan Agreement, Remedies,
        -------------------------                                      --------
is hereby amended by deleting existing subsections (a) and (b) thereof in their
entirety and by substituting the following in lieu thereof:

          "(a)  If an Event of Default specified in Section 8.1 (other than an
     Event of Default under Section 8.1(f) or (g) hereof) shall have occurred
     and shall be continuing, the Administrative Agent, at the request of the
     Majority Banks but subject to Section 9.8 hereof, shall (i) (A) terminate
     the Revolving Loan Commitment or any remaining Term Loan Commitment, and/or
     (B) declare the principal of and interest on the Loans and the Notes and
     all other amounts owed to the Banks and the Administrative Agent under this
     Agreement, the Notes and any other Loan Documents to be forthwith due and
     payable without presentment, demand, protest or other notice of any kind,
     all of which are hereby expressly waived, anything in this Agreement, the
     Notes or any other Loan Document to the contrary notwithstanding, and the
     Revolving Loan Commitment and any Term Loan Commitment shall thereupon
     forthwith terminate, and (ii) require the Borrower to, and the Borrower
     shall thereupon, deposit in an interest bearing account with the
     Administrative Agent, as cash collateral for the Obligations, an amount
     equal to the maximum amount currently or at any time thereafter available
     to be drawn on all outstanding Letters of Credit, and the Borrower hereby
     pledges to the Administrative Agent, the Banks and the Issuing Bank and
     grants to them a security interest in, all such cash as security for the
     Obligations.

          (b) Upon the occurrence and continuance of an Event of Default
     specified in Section 8.1(f) or (g) hereof, all principal, interest and
     other amounts due hereunder and under the Notes, and all other Obligations,
     shall thereupon and concurrently therewith become due and payable and the
     Revolving Loan Commitment shall forthwith terminate and the principal
     amount of the Loans outstanding hereunder shall bear interest at the
     Default Rate, and the Borrower shall thereupon forthwith deposit in an
     interest bearing account with the Administrative Agent, as cash collateral
     for the Obligations, an amount equal to the maximum amount currently or at
     any time thereafter available to be drawn on all outstanding Letters of
     Credit, all without any action by the Administrative Agent, the Banks, the
     Majority Banks, or any of them, and without presentment, demand, protest or
     other notice of any kind, all of which are expressly waived, anything in
     this Agreement or in the other Loan Documents to the contrary
     notwithstanding."

     (b) Section 8.2 of the Loan Agreement, Remedies, is hereby further amended
by adding the following new subsection 8.2(g) thereto:

                                      -14-
<PAGE>

          "(g) In the event that the Administrative Agent establishes a cash
     collateral account as contemplated by this Section 8.2, the Administrative
     Agent shall invest all funds in such account in such investments as the
     Administrative Agent in its sole and absolute discretion deems appropriate.
     The Borrower hereby acknowledges and agrees that any interest earned on
     such funds shall be retained by the Administrative Agent as additional
     collateral for the Obligations. Upon satisfaction in full of all
     Obligations, the Administrative Agent shall pay any amounts then held in
     such account to the Borrower."

     6. No Other Amendment or Waiver. Except for the amendments set forth above,
        ----------------------------
the text of the Loan Agreement and all other Loan Documents shall remain
unchanged and in full force and effect. No waiver by the Administrative Agent or
the Banks under the Loan Agreement or any other Loan Document is granted or
intended except as expressly set forth herein, and the Administrative Agent and
the Banks expressly reserve the right to require strict compliance in all other
respects (whether or not in connection with any Requests for Advance). Except as
set forth herein, the amendments agreed to herein shall not constitute a
modification of the Loan Agreement or any of the other Loan Documents, or a
course of dealing with the Administrative Agent and the Banks at variance with
the Loan Agreement or any of the other Loan Documents, such as to require
further notice by the Administrative Agent, the Banks or the Majority Banks to
require strict compliance with the terms of the Loan Agreement and the other
Loan Documents in the future.

     7. Representations and Warranties. The Borrower hereby represents
        ------------------------------
and warrants in favor of each of the Administrative Agent and each Bank that the
representations and warranties contained in Section 4.1 of the Loan Agreement
and contained in the other Loan Documents remain true and correct as of the date
hereof, both before and after giving effect to this Amendment, except to the
extent previously fulfilled in accordance with the terms of the Loan Agreement
or such other Loan Document, as applicable, or to the extent relating
specifically to the Agreement Date.  No Default now exists or will be caused
hereby.

     8. Condition Precedent. The effectiveness of this Amendment is subject to
        -------------------
the receipt by the Administrative Agent of counterparts hereof executed by the
Banks and the Borrower and of all documents, instruments, consents or items
which the Administrative Agent shall deem appropriate in connection herewith.

     9. Loan Documents. This document shall be deemed to be a Loan Document for
        --------------
all purposes under the Loan Agreement and the other Loan Documents.

     10. Counterparts. This Amendment may be executed in any number of
         ------------
counterparts, each of which shall be deemed to be an original, but all such
separate counterparts shall together constitute but one and the same instrument.

     11. Governing Law.  This Amendment shall be construed in accordance
         -------------
with and governed by the laws of the State of New York.

                                      -15-
<PAGE>

     12. Severability.  Any provision of this Amendment which is
         ------------
prohibited or unenforceable shall be ineffective to the extent of such
prohibition or unenforceability without invalidating the remaining provisions
hereof in that jurisdiction or affecting the validity or enforceability of such
provision in any other jurisdiction.

             [THE REMAINDER OF THIS PAGE INTENTIONALLY LEFT BLANK]

                                      -16-
<PAGE>

     IN WITNESS WHEREOF, the parties hereto have executed this Amendment or
caused it to be executed by their duly authorized officers, all as of the day
and year first above written.


BORROWERS:               AMERICAN TOWER, L.P.

                         By ATC GP INC.


                         By:  /s/ Joseph Winn
                              --------------------------------

                              Title:   Chief Financial Officer
                                    --------------------------


                         AMERICAN TOWERS, INC.


                         By:  /s/ Joseph Winn
                              ---------------------------------

                              Title:   Chief Financial Officer
                                    ---------------------------


ADMINISTRATIVE AGENT
AND BANKS:               TORONTO DOMINION (TEXAS), INC., as Administrative Agent
                         for itself and the Banks and as a Bank


                         By:  /s/ Jeffery R. Lents
                              ---------------------------------

                              Title:   Vice President
                                    ---------------------------



                         THE TORONTO-DOMINION BANK, NEW YORK BRANCH, as Issuing
                         Bank

                         By:  /s/ Jeffery R. Lents
                              ----------------------------------

                              Title:   Manager, Credit Administration
                                    ---------------------------------
<PAGE>

                         BANK OF AMERICA NATIONAL TRUST AND SAVINGS ASSOCIATION,
                         as a Bank


                         By:  /s/ Anthony M. Cacheria
                              -------------------------------------

                              Title:   Authorized Signatory
                                    -------------------------------


                         BANK OF MONTREAL, as a Bank


                         By:  /s/ Sarah Kim
                              -------------------------------------

                              Title:   Director
                                    -------------------------------


                         THE BANK OF NEW YORK, as a Bank


                         By:  /s/ Geoffrey C. Brooks
                              --------------------------------------

                              Title:   Vice President
                                    --------------------------------


                         THE BANK OF NOVA SCOTIA, as a Bank


                         By:  /s/ Paul A. Weissenberger
                              --------------------------------------

                              Title:   Authorized Signatory
                                    ---------------------------------


                         BANK OF SCOTLAND, as a Bank


                         By:  /s/ Janet Taffe
                              ---------------------------------------

                              Title:   Assistant Vice President
                                    ---------------------------------
<PAGE>

                         BANKBOSTON, N.A., as a Bank


                         By:  /s/ Lenny Mason
                              --------------------------------------

                              Title:   Director
                                    --------------------------------


                         BANKERS TRUST COMPANY, as a Bank


                         By:  /s/ Gregory Shefrin
                              --------------------------------------

                              Title:   Principal
                                    --------------------------------


                         BARCLAYS BANK, PLC, as a Bank


                         By:  /s/ Craig J. Lewis
                              --------------------------------------

                              Title:   Director
                                    --------------------------------


                         THE CHASE MANHATTAN BANK, as a Bank


                         By:  /s/ William E. Rottino
                              --------------------------------------

                              Title:   Vice President
                                    --------------------------------


                         THE CIT GROUP/EQUIPMENT FINANCING, INC., as a Bank


                         By:  /s/ J. E. Palmer
                              ---------------------------------------

                              Title:   Assistant Vice President
                                    ---------------------------------
<PAGE>

                         CITY NATIONAL BANK, as a Bank


                         By:  /s/ David J. Allen
                              --------------------------------------

                              Title:   Vice President
                                    --------------------------------


                         COBANK, ACB, as a Bank


                         By:  /s/ John Cole
                              --------------------------------------

                              Title:   Vice President
                                    --------------------------------


                         CREDIT LYONNAIS NEW YORK BRANCH, as a Bank


                         By:  /s/ Mark D. Thorsheim
                              --------------------------------------

                              Title:   Vice President
                                    --------------------------------


                         CREDIT SUISSE FIRST BOSTON, as a Bank


                         By:  /s/ Todd C. Morgan
                              --------------------------------------

                              Title:   Director
                                    --------------------------------


                         By:  /s/ Chris T. Horgan
                              ---------------------------------------

                              Title:   Vice President
                                    ---------------------------------


                         CRESTAR BANK, as a Bank


                         By:  /s/ Thomas Palmer
                              ---------------------------------------

                              Title:   Vice President
                                    ---------------------------------
<PAGE>

                         DRESDNER BANK AG, NEW YORK AND GRAND CAYMAN BRANCHES,
                         as a Bank


                         By:  /s/ Patrick A. Keleher
                              ---------------------------------------

                              Title:   Vice President
                                    ---------------------------------


                         By:  /s/ Brian E. Haughney
                              ---------------------------------------

                              Title:   Assistant Vice President
                                    ---------------------------------


                         FIRST NATIONAL BANK OF MARYLAND, as a Bank


                         By:  /s/ Christopher L. Smith
                              ----------------------------------------

                              Title:   Vice President
                                    ----------------------------------


                         FLEET NATIONAL BANK, as a Bank


                         By:  /s/ Amy B. Peden
                              -----------------------------------------

                              Title:   Assistant Vice President
                                    -----------------------------------


                         GENERAL ELECTRIC CAPITAL CORPORATION, as a Bank


                         By:  /s/ Mark F. Mylon
                              -----------------------------------------

                              Title:   Manager of Operations
                                    -----------------------------------
<PAGE>

                         THE HOWARD BANK, N.A., as a Bank


                         By:  /s/ Michael W. Quinn
                              ----------------------------------------

                              Title:   Senior Vice President
                                    ----------------------------------


                         KEY CORPORATE CAPITAL INC., as a Bank


                         By:  /s/ Kenneth J. Keeler
                              ---------------------------------------

                              Title:   Senior Vice President
                                    ---------------------------------


                         LEHMAN COMMERCIAL PAPER INC., as a Bank


                         By:  /s/ Michele Swanson
                              ---------------------------------------

                              Title:   Authorized Signatory
                                    ---------------------------------


                         MELLON BANK, N.A., as a Bank


                         By:  /s/ Henry S. Beukema
                              ---------------------------------------

                              Title:   Assistant Vice President
                                    ---------------------------------


                         MERCANTILE BANK NATIONAL ASSOCIATION, as a Bank


                         By:  /s/ John H. Phillips
                              ---------------------------------------

                              Title:   Vice President
                                    ---------------------------------
<PAGE>

                         THE MITSUBISHI TRUST AND BANKING CORPORATION, as a Bank


                         By:  /s/ Beatrice E. Kossodo
                              ---------------------------------------

                              Title:   Senior Vice President
                                    ---------------------------------


                         NATIONAL BANK OF CANADA, as a Bank


                         By:  /s/ Theresa White
                              ---------------------------------------

                              Title:   Vice President
                                    ---------------------------------


                         By:  /s/ James Drum
                              ---------------------------------------

                              Title:   Vice President
                                    ---------------------------------


                         PNC BANK, NATIONAL ASSOCIATION, as a Bank


                         By:  /s/ Kristen E. Talaber
                              ---------------------------------------

                              Title:   Vice President
                                    ---------------------------------


                         STATE STREET BANK AND TRUST COMPANY, as a Bank


                         By:  /s/ Edward C. Thaute
                              ----------------------------------------

                              Title:   Vice President
                                    ----------------------------------
<PAGE>

                         UNION BANK OF CALIFORNIA, N.A., as a Bank


                         By:  /s/ Stender E. Sweeney
                              ----------------------------------------

                              Title:   Assistant Vice President
                                    ----------------------------------


                         US TRUST, as a Bank


                         By:  /s/ Daniel G. Eastman
                              ---------------------------------------

                              Title:   Vice President
                                    ---------------------------------


                         WEBSTER BANK, as a Bank


                         By:
                            -----------------------------------------

                              Title:
                                    ---------------------------------

<PAGE>

                                                                    EXHIBIT 10.2
                                                                    ------------
                 FOURTH AMENDMENT TO FACILITY A LOAN AGREEMENT
                                  AND CONSENT

     THIS FOURTH AMENDMENT TO FACILITY A LOAN AGREEMENT AND CONSENT (this
"Amendment and Consent"), dated as of the 29th day of September, 1999 (the
 ---------------------
"Amendment Date"), by and among AMERICAN TOWER, L.P., a Delaware limited
 --------------
partnership, and AMERICAN TOWERS, INC., a Delaware corporation (collectively,
the "Borrower"), the FINANCIAL INSTITUTIONS SIGNATORY HERETO and TORONTO
     -------
DOMINION (TEXAS), INC., as administrative agent (the "Administrative Agent") for
                                                      --------------------
the Banks (as defined in the Loan Agreement defined below);


                              W I T N E S S E T H:
                              -------------------

     WHEREAS, the Borrower, the Banks and the Administrative Agent are parties
to that certain ATS Facility A Loan Agreement dated as of June 16, 1998, as
amended by that certain First Amendment to ATS Facility A Loan Agreement dated
as of October 30, 1998, that certain Second Amendment and Waiver to ATS Facility
A Loan Agreement dated as of February 8, 1999 and that certain Third Amendment
to ATS Facility A Loan Agreement dated as of July 9, 1999 (as amended, modified,
supplemented and restated from time to time, the "Loan Agreement"); and
                                                  --------------

     WHEREAS, the Borrower has requested, and the Banks have agreed, on the
terms and subject to the conditions set forth herein, to permit the Parent (as
defined in the Loan Agreement) to incur certain indebtedness and to prepay the
principal amount of Indebtedness outstanding under the Parent Loan Agreement (as
defined in the Loan Agreement) and to make certain other amendments to the Loan
Agreement, in each case, as provided herein;

     NOW, THEREFORE, in consideration of the premises set forth above, the
covenants and agreements hereinafter set forth, and other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged, the
parties hereto agree that all capitalized terms used herein shall have the
meanings ascribed thereto in the Loan Agreement, and further agree as follows:

     1.   Amendment to Article 1. Article 1 of the Loan Agreement, Definitions,
          ----------------------                                   -----------
is hereby amended by adding the following definition of "Convertible Notes,"
                                                         -----------------
thereto in appropriate alphabetical order:

           "'Convertible Notes' shall mean convertible notes issued by the
             -----------------
     Parent having the following terms: (a) such Convertible Notes shall be
     overfunded by an amount equal to all interest payable with respect thereto
     for the period commencing on the date of issuance thereof through the
     second anniversary of the date of issuance, (b) no principal payments
     (other than in common stock of the Parent) on the Convertible Notes may be
<PAGE>

     required until six (6) months after the Maturity Date, (c) the proceeds
     (other than any amount required to pay interest during any applicable
     overfunding period) of such Convertible Notes shall be contributed as
     equity to the Co-Borrowers to be applied to the Loans in accordance with
     the provisions of this Agreement with any remaining proceeds used to pay in
     full all outstanding amounts under the Parent Loan Agreement in accordance
     with that certain Fourth Amendment to Facility A Loan Agreement and Consent
     dated as of September 29, 1999, (d) not guaranteed by Subsidiaries of the
     Parent and (e) such Convertible Notes shall be unsecured and have such
     other terms and conditions substantially as set forth in the Offering
     Memorandum with respect thereto."

     2.   Amendment to Article 8. Section 8.1 of the Loan Agreement, Events of
          ----------------------                                     ---------
Default, is hereby amended by deleting subsection (q) thereof in its entirety
- -------
and by substituting the following in lieu thereof:

     "(q) The Parent shall incur or permit to remain outstanding any
          Indebtedness for Money Borrowed other than the Convertible Notes (or
          any refinancing of the foregoing which does not exceed the principal
          amount outstanding on the date of such refinancing); or"

     3.   Consent to Prepayment under Parent Loan Agreement. This Amendment and
          -------------------------------------------------
Consent, when executed by the Majority Banks and accepted by the Borrower, will,
subject to the terms and conditions hereof, reflect the Banks' consent to the
prepayment by the Parent in full of all amounts outstanding under the Parent
Loan Agreement solely with a portion the proceeds of the Convertible Notes
remaining after application of such proceeds as required by Article 2 of the
Loan Agreement; provided, however, that prior to such prepayment, the Co-
                -----------------
Borrowers apply the proceeds of the Convertible Notes (other than any amount
required to pay interest during any applicable overfunding period) as required
by Article 2 of the Loan Agreement.

     4.   No Other Amendment or Consent. Except for the amendments and consent
          -----------------------------
set forth above, the text of the Loan Agreement and all other Loan Documents
shall remain unchanged and in full force and effect. No waiver or consent by the
Administrative Agent or the Banks under the Loan Agreement or any other Loan
Document is granted or intended except as expressly set forth herein, and the
Administrative Agent and the Banks expressly reserve the right to require strict
compliance in all other respects (whether or not in connection with any Requests
for Advance). Except as set forth herein, the amendments and consent agreed to
herein shall not constitute a modification of the Loan Agreement or any of the
other Loan Documents, or a course of dealing with the Administrative Agent and
the Banks at variance with the Loan Agreement or any of the other Loan
Documents, such as to require further notice by the Administrative Agent, the
Banks or the Majority Banks to require strict compliance with the terms of the
Loan Agreement and the other Loan Documents in the future.

     5.   Loan Documents. This Amendment and Consent shall be deemed to be a
          --------------
Loan Document for all purposes under the Loan Agreement and the other Loan
Documents.

                                      -2-
<PAGE>

     6.   Counterparts. This Amendment and Consent may be executed in any number
          ------------
of counterparts, each of which shall be deemed to be an original, but all such
separate counterparts shall together constitute but one and the same instrument.

     7.   Governing Law. This Amendment and Consent shall be construed in
          -------------
accordance with and governed by the laws of the State of New York.

     8.   Severability. Any provision of this Amendment and Consent which is
          ------------
prohibited or unenforceable shall be ineffective to the extent of such
prohibition or unenforceability without invalidating the remaining provisions
hereof in that jurisdiction or affecting the validity or enforceability of such
provision in any other jurisdiction.

             [THE REMAINDER OF THIS PAGE INTENTIONALLY LEFT BLANK]

                                      -3-
<PAGE>

     IN WITNESS WHEREOF, the parties hereto have executed this Amendment and
Consent or caused it to be executed by their duly authorized officers, all as of
the day and year first above written.


BORROWERS:               AMERICAN TOWER, L.P.

                         By ATC GP INC.


                         By:  /s/ Joseph L. Winn
                            ---------------------------------------

                              Title:   Chief Financial Officer


                         AMERICAN TOWERS, INC.


                         By:  /s/ Joseph L. Winn
                            ---------------------------------------

                              Title:   Chief Financial Officer


ADMINISTRATIVE AGENT
AND BANKS:               TORONTO DOMINION (TEXAS), INC., as Administrative Agent
                         for itself and the Banks and as a Bank


                         By:  /s/ Jeffrey R. Lents
                            ---------------------------------------

                              Title:   Vice President



                         THE TORONTO-DOMINION BANK, NEW YORK BRANCH, as Issuing
                         Bank

                         By:  /s/ Jeffrey R. Lents
                            ---------------------------------------

                              Title: Manager, Credit Administration
                                     ------------------------------
<PAGE>

                         BANK OF AMERICA, N.A. (formerly known as Bank of
                         America National Trust and Savings Association), as a
                         Bank


                         By: /s/ Todd Shipley
                            ---------------------------------------

                              Title: Senior Vice President
                                    -------------------------------


                         BANK OF MONTREAL, as a Bank


                         By: /s/ Sarah Kim
                            ---------------------------------------

                              Title: Director
                                     ------------------------------


                         THE BANK OF NEW YORK, as a Bank


                         By: /s/ Geoffrey C. Brooks
                            ---------------------------------------

                              Title: Vice President
                                    -------------------------------


                         THE BANK OF NOVA SCOTIA, as a Bank


                         By: /s/ Paul A. Weissenberger
                            ---------------------------------------

                              Title: Authorized Signatory
                                    -------------------------------


                         BANK OF SCOTLAND, as a Bank


                         By: /s/ Annie Glynn
                            ---------------------------------------

                              Title: Senior Vice President
                                    -------------------------------
<PAGE>

                         BANKBOSTON, N.A., as a Bank


                         By: /s/ Lenny Mason
                             ---------------------------------------

                              Title: Director
                                     -------------------------------


                         BANKERS TRUST COMPANY, as a Bank


                         By: /s/ Gregory Shefrin
                             ---------------------------------------

                              Title: Principal
                                     -------------------------------


                         BARCLAYS BANK, PLC, as a Bank


                         By: /s/ Craig J. Lewis
                             ---------------------------------------

                              Title: Director
                                    -------------------------------


                         THE CHASE MANHATTAN BANK, as a Bank


                         By: /s/ William E. Rottino
                             ---------------------------------------

                              Title: Vice President
                                     -------------------------------


                         THE CIT GROUP/EQUIPMENT FINANCING, INC., as a Bank


                         By: /s/ Daniel E. A. Nichols
                             ---------------------------------------

                              Title: Assistant Vice President
                                     -------------------------------
<PAGE>

                         CITY NATIONAL BANK, as a Bank


                         By: /s/ Rod Bollins
                             --------------------------------------

                              Title: Vice President
                                     ------------------------------


                         COBANK, ACB, as a Bank


                         By: /s/ Teresa L. Fountain
                             ---------------------------------------

                              Title: Assistant Corporate Secretary
                                     -------------------------------


                         CREDIT LYONNAIS NEW YORK BRANCH, as a Bank


                         By: /s/ Mark Campellone
                            ---------------------------------------

                              Title: First Vice President
                                     ------------------------------


                         CREDIT SUISSE FIRST BOSTON, as a Bank


                         By: /s/ Todd C. Morgan
                             --------------------------------------

                              Title: Director
                                     ------------------------------


                         By: /s/ Kristin Lepri
                             --------------------------------------

                              Title: Associate
                                    -------------------------------
<PAGE>

                         CRESTAR BANK, as a Bank


                         By: /s/ Edwin D. Brooks, Jr.
                             ---------------------------------------

                              Title: Executive Vice President
                                     -------------------------------


                         DRESDNER BANK AG, NEW YORK AND GRAND CAYMAN BRANCHES,
                         as a Bank


                         By: /s/ Constance Loosemore
                             ---------------------------------------

                              Title: Assistant Vice President
                                     -------------------------------


                         By: /s/ Patrick A. Keleher
                             ---------------------------------------

                              Title: Vice President
                                     -------------------------------


                         ALLFIRST BANK, as a Bank


                         By: /s/ W. Blake Hampson
                             ---------------------------------------

                              Title: Vice President
                                     -------------------------------


                         FLEET NATIONAL BANK, as a Bank


                         By: /s/ Jeffrey R. Greene
                             ---------------------------------------

                              Title: Vice President
                                     -------------------------------
<PAGE>

                         THE FUJI BANK, LIMITED, as a Bank


                         By: /s/ Kazuyuki Nishimura
                             ---------------------------------------

                              Title: Senior Vice President and Group Head
                                     ------------------------------------


                         GENERAL ELECTRIC CAPITAL CORPORATION, as a Bank


                         By: /s/ Michael J. Tzougrakis
                             ---------------------------------------

                              Title: Manager of Operations
                                     -------------------------------


                         THE HOWARD BANK, N.A., as a Bank


                         By: /s/ Michael W. Quinn
                             ---------------------------------------

                              Title: Senior Vice President
                                     -------------------------------


                         KEY CORPORATE CAPITAL INC., as a Bank


                         By: /s/ Jason R. Weaver
                             ---------------------------------------

                              Title: Vice President
                                     -------------------------------



<PAGE>

                         MELLON BANK, N.A., as a Bank


                         By: /s/ Henry Beukema
                             ---------------------------------------

                              Title: Assistant Vice President
                                     -------------------------------


                         MERCANTILE BANK NATIONAL ASSOCIATION, as a Bank


                         By: /s/ John H. Phillips
                             ---------------------------------------

                              Title: Vice President
                                     -------------------------------


                         THE MITSUBISHI TRUST AND BANKING CORPORATION, as a Bank


                         By: /s/ Toshihiro Hayashi
                             ---------------------------------------

                              Title: Senior Vice President
                                     -------------------------------


                         NATIONAL BANK OF CANADA, as a Bank


                         By: /s/ Theresa White
                             ---------------------------------------

                              Title: Vice President
                                     -------------------------------


                         By: /s/ Vincent Lima
                             ---------------------------------------

                              Title: Vice President
                                     -------------------------------
<PAGE>

                         PNC BANK, NATIONAL ASSOCIATION, as a Bank


                         By: /s/ Kristen E. Talaber
                             ---------------------------------------

                              Title: Vice President
                                     -------------------------------


                         STATE STREET BANK AND TRUST COMPANY, as a Bank


                         By: /s/ Edware C. Thaute
                             ---------------------------------------

                              Title: Vice President
                                     -------------------------------


                         UNION BANK OF CALIFORNIA, N.A., as a Bank


                         By: /s/ Darren H. Miyata
                             ---------------------------------------

                              Title: Assistant Vice President
                                     -------------------------------


                         US TRUST, as a Bank


                         By: /s/ Daniel G. Eastman
                             ---------------------------------------

                              Title: Vice President
                                     -------------------------------


                         WEBSTER BANK, as a Bank


                         By: /s/ Juliana B. Dalton
                             ---------------------------------------

                              Title: Vice President
                                     -------------------------------

<PAGE>

                                                                    EXHIBIT 10.3
                                                                    ------------
                                THIRD AMENDMENT
                                       TO
                         ATS FACILITY B LOAN AGREEMENT

     THIS THIRD AMENDMENT TO ATS FACILITY B LOAN AGREEMENT (this "Amendment"),
                                                                  ---------
dated as of the 27th day of May, 1999 (the "Amendment Date"), by and among
                                            --------------
AMERICAN TOWER, L.P., a Delaware limited partnership, and AMERICAN TOWERS, INC.,
a Delaware corporation (collectively, the "Borrower"), the FINANCIAL
                                           --------
INSTITUTIONS SIGNATORY HERETO and TORONTO DOMINION (TEXAS), INC., as
administrative agent (the "Administrative Agent") for the Banks (as defined in
                           --------------------
the Loan Agreement defined below);


                              W I T N E S S E T H:
                              -------------------


     WHEREAS, the Borrower, the Banks and the Administrative Agent are parties
to that certain ATS Facility B Loan Agreement dated as of June 16, 1998, as
amended by that certain First Amendment to ATS Facility B Loan Agreement dated
as of October 30, 1998 and that certain Second Amendment and Waiver to ATS
Facility B Loan Agreement dated as of February 8, 1999 (as amended, modified,
supplemented and restated from time to time, the "Loan Agreement"); and
                                                  --------------

     WHEREAS, the Borrower has informed Administrative Agent and the Banks that
it would like to extend the Termination Date of the Facility B Commitment by a
364-day period; and

     WHEREAS, the Borrower, the Administrative Agent and the Banks have agreed
to extend the Termination Date of the Facility B Commitment by a 364-day period
on the terms and conditions set forth herein;

     NOW, THEREFORE, in consideration of the premises set forth above, the
covenants and agreements hereinafter set forth, and other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged, the
parties hereto agree that all capitalized terms used herein shall have the
meanings ascribed thereto in the Loan Agreement, and further agree as follows:

     1.   Amendment to Article 1. Article 1 of the Loan Agreement, Definitions,
          ----------------------
is hereby amended by deleting the definition "Termination Date" in its entirety
and by substituting in lieu thereof the following:

     "'Termination Date' shall mean June 14, 2000."
       -----------------
<PAGE>

     2.   Amendment to Article 2.  Section 2.4 of the Loan Agreement,
          ----------------------
Commitment Fees, is hereby amended by deleting such section in its entirety and
by substituting in lieu thereof the following:

          "Section 2.4 Commitment Fees. Commencing on May 27, 1999 and at all
           ---------------------------
     times thereafter, the Borrowers agree to pay, on a joint and several basis,
     to the Administrative Agent for the account of each of the Banks in
     accordance with such Bank's respective Facility B Commitment Ratio, a
     commitment fee on the aggregate unborrowed balance of the Facility B
     Commitment for each day from May 27, 1999 until the Termination Date, or,
     if applicable, the Maturity Date, at a rate of one-quarter of one percent
     (0.250%) per annum. Such commitment fee shall be computed on the basis of a
     year of 365/366 days for the actual number of days elapsed, shall be
     payable quarterly in arrears on the last Business Day of each calendar
     quarter, and shall be fully earned when due and non-refundable when paid. A
     final payment of any commitment fee then payable shall also be due and
     payable on the Termination Date, or, if applicable, the Maturity Date."

     3.   No Other Amendment or Waiver.  Except for the amendments set
          ----------------------------
forth above, the text of the Loan Agreement and all other Loan Documents shall
remain unchanged and in full force and effect.  No waiver by the Administrative
Agent or the Banks under the Loan Agreement or any other Loan Document is
granted or intended except as expressly set forth herein, and the Administrative
Agent and the Banks expressly reserve the right to require strict compliance in
all other respects (whether or not in connection with any Requests for Advance).
Except as set forth herein, the amendment agreed to herein shall not constitute
a modification of the Loan Agreement or any of the other Loan Documents, or a
course of dealing with the Administrative Agent and the Banks at variance with
the Loan Agreement or any of the other Loan Documents, such as to require
further notice by the Administrative Agent, the Banks or the Majority Banks to
require strict compliance with the terms of the Loan Agreement and the other
Loan Documents in the future.

     4.   Representations and Warranties.  The Borrower hereby represents
          ------------------------------
and warrants in favor of each of the Administrative Agent and each Bank that the
representations and warranties contained in Section 4.1 of the Loan Agreement
and contained in the other Loan Documents remain true and correct as of the date
hereof, both before and after giving effect to this Amendment and Waiver, except
to the extent previously fulfilled in accordance with the terms of the Loan
Agreement or such other Loan Document, as applicable, or to the extent relating
specifically to the Agreement Date.  No Default now exists or will be caused
hereby.

     5.   Condition Precedent.  The effectiveness of this Amendment and
          -------------------
Waiver is subject to the receipt by the Administrative Agent of counterparts
hereof executed by the Banks and the Borrower and of all documents, instruments,
consents or items which the Administrative Agent shall deem appropriate in
connection herewith.

     6.   Loan Documents. This document shall be deemed to be a Loan Document
          --------------
for all purposes under the Loan Agreement and the other Loan Documents.

                                      -2-
<PAGE>

     7.   Counterparts. This Amendment and Waiver may be executed in any
          ------------
number of counterparts, each of which shall be deemed to be an original, but all
such separate counterparts shall together constitute but one and the same
instrument.

     8.   Governing Law.  This Amendment and Waiver shall be construed in
          -------------
accordance with and governed by the laws of the State of New York.

     9.   Severability.  Any provision of this Amendment and Waiver which
          ------------
is prohibited or unenforceable shall be ineffective to the extent of such
prohibition or unenforceability without invalidating the remaining provisions
hereof in that jurisdiction or affecting the validity or enforceability of such
provision in any other jurisdiction.

             [THE REMAINDER OF THIS PAGE INTENTIONALLY LEFT BLANK]

                                      -3-
<PAGE>

  IN WITNESS WHEREOF, the parties hereto have executed this Amendment or caused
it to be executed by their duly authorized officers, all as of the day and year
first above written.


BORROWERS:               AMERICAN TOWER, L.P.

                         By ATC GP INC.


                         By:  /s/ Joseph Winn
                              -----------------------------------

                              Title:   Chief Financial Officer
                                    -----------------------------


                         AMERICAN TOWERS, INC.


                         By:  /s/ Joseph Winn
                              ----------------------------------

                              Title:   Chief Financial Officer
                                    ----------------------------


ADMINISTRATIVE AGENT
AND BANKS:               TORONTO DOMINION (TEXAS), INC., as Administrative Agent
                         for itself and the Banks and as a Bank


                         By:  /s/ Jeffery R. Lents
                              ------------------------------------

                              Title:   Vice President
                                    ------------------------------


                         BANK OF AMERICA NATIONAL TRUST AND SAVINGS ASSOCIATION,
                         as a Bank


                         By:  /s/ Fred L. Thorne
                              -----------------------------------

                              Title:   Vice President
                                    -----------------------------
<PAGE>

                         BANK OF MONTREAL, as a Bank


                         By:  /s/ Sarah Kim
                              --------------------------------------

                              Title:   Director
                                    --------------------------------


                         THE BANK OF NEW YORK, as a Bank


                         By:  /s/ Geoffrey C. Brooks
                              --------------------------------------

                              Title:   Vice President
                                    --------------------------------


                         THE BANK OF NOVA SCOTIA, as a Bank


                         By:  /s/ Paul A. Weissenberger
                              ---------------------------------------

                              Title:   Authorized Signatory
                                    ---------------------------------


                         BANK OF SCOTLAND, as a Bank


                         By:  /s/ Janet Taffe
                              ---------------------------------------

                              Title:   Assistant Vice President
                                    ---------------------------------


                         BANKBOSTON, N.A., as a Bank


                         By:  /s/ Lenny Mason
                              ---------------------------------------

                              Title:   Director
                                    ---------------------------------
<PAGE>

                         BANKERS TRUST COMPANY, as a Bank


                         By:  /s/ Gregory Shefrin
                              --------------------------------------

                              Title:   Principal
                                    --------------------------------


                         BARCLAYS BANK, PLC, as a Bank


                         By:  /s/ Craig J. Lewis
                              --------------------------------------

                              Title:   Director
                                    --------------------------------


                         THE CHASE MANHATTAN BANK, as a Bank


                         By:  /s/ William E. Rottino
                              ---------------------------------------

                              Title:   Vice President
                                    ---------------------------------


                         THE CIT GROUP/EQUIPMENT FINANCING, INC., as a Bank


                         By:  /s/ Barry L. Blailock
                              ---------------------------------------

                              Title:   Assistant Vice President/Credit
                                    ----------------------------------


                         CITY NATIONAL BANK, as a Bank


                         By:  /s/ David J. Allen
                              ----------------------------------

                              Title:   Vice President
                                    ----------------------------
<PAGE>

                         COBANK, ACB, as a Bank


                         By:  /s/ John P. Cole
                              ----------------------------------

                              Title:   Vice President
                                    ----------------------------


                         CREDIT LYONNAIS NEW YORK BRANCH, as a Bank


                         By:  /s/ Mark Campalone
                              ----------------------------------

                              Title:   First Vice President
                                    ----------------------------


                         CREDIT SUISSE FIRST BOSTON, as a Bank


                         By:  /s/ Bill O'Daly
                              ----------------------------------

                              Title:   Vice President
                                    ----------------------------


                         By:  /s/ Kristin Lepri
                              ----------------------------------

                              Title:   Associate
                                    ----------------------------


                         CRESTAR BANK, as a Bank


                         By:  /s/ LaTarnya B. Mason
                              ----------------------------------

                              Title:   Assistant Vice President
                                    ----------------------------
<PAGE>

                         DRESDNER BANK AG, NEW YORK AND GRAND CAYMAN BRANCHES,
                         as a Bank


                         By:
                              ----------------------------------

                              Title:
                                    ----------------------------


                         By:
                              ----------------------------------

                              Title:
                                    ----------------------------


                         FIRST NATIONAL BANK OF MARYLAND, as a Bank


                         By:  /s/ W. Blake Hampson
                              ----------------------------------

                              Title:   Vice President
                                    ----------------------------


                         FLEET NATIONAL BANK, as a Bank


                         By:
                              -----------------------------------

                              Title:
                                    -----------------------------


                         GENERAL ELECTRIC CAPITAL CORPORATION, as a Bank


                         By:  /s/ Mark F. Mylon
                              -----------------------------------

                              Title:   Manager-Operations
                                    -----------------------------
<PAGE>

                         THE HOWARD BANK, N.A., as a Bank


                         By:  /s/ Michael W. Quinn
                              ------------------------------------

                              Title:   Senior Vice President
                                    ------------------------------


                         KEY CORPORATE CAPITAL INC., as a Bank


                         By:  /s/ Jason R. Weaver
                              ------------------------------------

                              Title:   Vice President
                                    ------------------------------


                         LEHMAN COMMERCIAL PAPER INC., as a Bank


                         By:  /s/ Michele Swanson
                              ------------------------------------

                              Title:   Authorized Signatory
                                    ------------------------------


                         MELLON BANK, N.A., as a Bank


                         By:  /s/ Henry S. Beukema
                              ------------------------------------

                              Title:   Assistant Vice President
                                    ------------------------------


                         MERCANTILE BANK NATIONAL ASSOCIATION, as a Bank


                         By:  /s/ John H. Phillips
                              -----------------------------------

                              Title:   Vice President
                                    -----------------------------
<PAGE>

                         THE MITSUBISHI TRUST AND BANKING CORPORATION, as a Bank


                         By:  /s/ Toshihiro Hayashi
                              -----------------------------------

                              Title:  Senior Vice President
                                    -----------------------------


                         NATIONAL BANK OF CANADA, as a Bank


                         By:  /s/ Theresa White
                              -----------------------------------

                              Title:   Vice President
                                    -----------------------------


                         By:  /s/ Gaetan Frosina
                              -----------------------------------

                              Title:   Vice President
                                    -----------------------------


                         PNC BANK, NATIONAL ASSOCIATION, as a Bank


                         By:  /s/ Kristen E. Talaber
                              ----------------------------------

                              Title:   Vice President
                                    ----------------------------


                         STATE STREET BANK AND TRUST COMPANY, as a Bank


                         By:  /s/ Greg Spurr
                              ---------------------------------

                              Title:   Vice President
                                    ----------------------------
<PAGE>

                         UNION BANK OF CALIFORNIA, N.A., as a Bank


                         By:  /s/ Stender E. Sweeney
                              ----------------------------------

                              Title:   Assistant Vice President
                                    ----------------------------


                         US TRUST, as a Bank


                         By:
                              ----------------------------------

                              Title:
                                    ----------------------------


                         WEBSTER BANK, as a Bank


                         By:  /s/ Juliana B.Dalton
                              ---------------------------------

                              Title:   Vice President
                                    ----------------------------

<PAGE>
                                                                    EXHIBIT 10.4
                                                                    ------------
                                FOURTH AMENDMENT
                                       TO
                         ATS FACILITY B LOAN AGREEMENT


  THIS FOURTH AMENDMENT TO ATS FACILITY B LOAN AGREEMENT (this "Amendment"),
                                                                ---------
dated as of the 9th  day of July, 1999 (the "Amendment Date"), by and among
                                             --------------
AMERICAN TOWER, L.P., a Delaware limited partnership, and AMERICAN TOWERS, INC.,
a Delaware corporation (collectively, the "Borrower"), the FINANCIAL
                                           --------
INSTITUTIONS SIGNATORY HERETO and TORONTO DOMINION (TEXAS), INC., as
administrative agent (the "Administrative Agent") for the Banks (as defined in
                           --------------------
the Loan Agreement defined below);

                              W I T N E S S E T H:
                              -------------------

   WHEREAS, the Borrower, the Banks and the Administrative Agent are parties to
that certain ATS Facility B Loan Agreement dated as of June 16, 1998, as amended
by that certain First Amendment to ATS Facility B Loan Agreement dated as of
October 30, 1998, that certain Second Amendment and Waiver to ATS Facility B
Loan Agreement dated as of February 8, 1999 and that certain Third Amendment to
ATS Facility B Loan Agreement dated as of May 27, 1999 (as amended, modified,
supplemented and restated from time to time, the "Loan Agreement"); and
                                                  --------------

   WHEREAS, the Borrower has requested, and the Banks have agreed, on the terms
and subject to the conditions set forth herein, to make certain amendments to
the Loan Agreement as provided herein;

   NOW, THEREFORE, in consideration of the premises set forth above, the
covenants and agreements hereinafter set forth, and other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged, the
parties hereto agree that all capitalized terms used herein shall have the
meanings ascribed thereto in the Loan Agreement, and further agree as follows:

    1.  Amendments to Article 1.
        -----------------------

    (a) Article 1 of the Loan Agreement, Definitions, is hereby amended by
adding the following new definitions of "Broker/Dealer" and "communications
                                         -------------       --------------
site" thereto in appropriate alphabetical order:
- ----
<PAGE>

          "'Broker/Dealer' shall mean, with respect to any Investment or
            -------------
     Acquisition permitted under Section 7.6(a) hereof, (a) any broker/dealer
     (acting as principal) registered as a broker or a dealer under Section 15
     of the Exchange Act, the unsecured short-term debt obligations of which are
     rated "P-1" by Moody's Investors Service, Inc. and at least "A-1" by
     Standard and Poor's Ratings Group, a division of The McGraw-Hill Companies,
     Inc., at the time of entering into such Investment or Acquisition or (b) an
     unrated, broker/dealer, acting as principal, that is a wholly-owned
     Subsidiary of a non-bank or bank holding company, the unsecured short-term
     debt obligations of which are rated "P-1" by Moody's Investors Service,
     Inc. and at least "A-1" by Standard and Poor's Ratings Group, a division of
     The McGraw-Hill Companies, Inc., at the time of entering into such
     Investment or Acquisition."

          "'communications site' shall mean (a) any undeveloped real property
            -------------------
     and (b) communication towers which have no bona fide customers on the date
     of acquisition thereof."


     (b)  Article 1 of the Loan Agreement, Definitions, is hereby amended by
                                           -----------
deleting the definitions of "Fixed Charges Coverage Ratio" and "Subsidiary" in
                             ----------------------------       ----------
their entirety and by substituting the following in lieu thereof in appropriate
alphabetical order:

          "'Fixed Charges Coverage Ratio' shall mean, as of any calculation
            ----------------------------
     date, the ratio of (a) the sum of (i) Annualized Operating Cash Flow as of
     the most recently completed fiscal quarter, plus (ii) the sum of (A) the
                                                 ----
     amount of unused Commitments as of such date under this Agreement and the
     ATS Facility A Loan Agreement which could be borrowed on such date in
     compliance with Section 7.8 hereof, plus, (B) to the extent then reflected
                                         ----
     as net cash on the balance sheet of either Borrower, the net cash proceeds
     of any equity issued, directly or indirectly, by either Borrower and
     received by either Borrower from the Parent (after deducting any portion
     thereof applied to the Loans or the Facility A Loans) to (b) Fixed
     Charges."

          "'Subsidiary' shall mean, as applied to any Person, (a) any
            ----------
     corporation of which no less than fifty percent (50%) of the outstanding
     stock (other than directors' qualifying shares) having ordinary voting
     power to elect a majority of its board of directors, regardless of the
     existence at the time of a right of the holders of any class or classes of
     securities of such corporation to exercise such voting power by reason of
     the happening of any contingency, or any partnership of which no less than
     fifty percent (50%) of the outstanding partnership interests, is at the
     time owned directly or indirectly by such Person, or by one or more
     Subsidiaries of such Person, or by such Person and one or more Subsidiaries
     of such Person, provided, however, that if such Person and/or such Person's
                     --------  -------
     Subsidiaries directly or indirectly own no more than fifty percent (50%) of
     such Subsidiary's ownership interests, then such Subsidiary's operating or
     governing documents must require (i) such Subsidiary's net cash after the
     establishment of reserves be distributed to its equity holders no less
     frequently than quarterly and (ii) the consent of such Person and/or such
     Person's Subsidiaries to amend or otherwise modify the

                                      -2-
<PAGE>

     provisions of such operating or governing documents requiring such
     distributions, or (b) any other entity which is directly or indirectly
     controlled or capable of being controlled by such Person, or by one or more
     Subsidiaries of such Person, or by such Person and one or more Subsidiaries
     of such Person."

     2.  Amendment to Article 7. Section 7.6 of the Loan Agreement, Investments
         ----------------------                                     -----------
and Acquisitions, is hereby amended by deleting subsections (a), (b) and (c)
- ----------------
thereof in their entirety and by substituting the following in lieu thereof:

               "(a) directly or through a brokerage account or investment
          adviser (i) purchase marketable, direct obligations of the United
          States of America, its agencies and instrumentalities maturing within
          three hundred sixty-five (365) days of the date of purchase, (ii)
          purchase commercial paper and other short-term obligations and
          business savings accounts issued by corporations, each of which shall
          have a combined net worth of at least $100,000,000 and each of which
          conducts a substantial part of its business in the United States of
          America, maturing within two hundred seventy (270) days from the date
          of the original issue thereof, and whose issuer is, at the time of
          purchase, rated "P-2" or better by Moody's Investors Service, Inc. or
          "A-2" or better by Standard and Poor's Ratings Group, a division of
          The McGraw-Hill Companies, Inc., (iii) purchase repurchase agreements,
          bankers' acceptances, and domestic and Eurodollar certificates of
          deposit maturing within three hundred sixty-five (365) days of the
          date of purchase which are issued by, or time deposits maintained
          with, (A) a United States national or state bank (or any domestic
          branch of a foreign bank) subject to supervision and examination by
          federal or state banking or depository institution authorities and
          having capital, surplus and undivided profits totaling more than
          $100,000,000 and rated "A" or better by Moody's Investors Service,
          Inc. or Standard and Poor's Ratings Group, a division of The McGraw-
          Hill, Companies, Inc., or (B) a Broker/Dealer, and (iv) invest in
          money market funds having a rating from Moody's Investors Service,
          Inc. and Standard and Poor's Ratings Group, a division of The McGraw-
          Hill, Companies, Inc. in the highest investment category granted
          thereby;

               (b) so long as no Default then exists or would be caused thereby,
          establish Unrestricted Subsidiaries and make Investments in such
          Unrestricted Subsidiaries of up to, in the aggregate, at any time, the
          sum of (i) $60,000,000 with loans borrowed under this Agreement or the
          ATS Facility B Loan Agreement, and (ii) equity proceeds not used to
          pay the Separation Obligations or to make Investments permitted under
          Sections 7.6(c) and (d) hereof;

               (c) so long as no Default then exists or would be caused thereby,
          and subject to compliance with Section 5.13 hereof, make Acquisitions;
          provided, however, that Acquisitions of communications sites, tower
          --------  -------
          management businesses and other services businesses, such as
          construction and teleport

                                      -3-
<PAGE>

          businesses, shall not exceed, in the aggregate, at any time, the sum
          of (i) $50,000,000 and (ii) equity proceeds not used to pay the
          Separation Obligations after the Agreement Date or to make Investments
          permitted under Sections 7.6(b) and (d) hereof;"

     3.   No Other Amendment or Waiver. Except for the amendments set forth
          ----------------------------
above, the text of the Loan Agreement and all other Loan Documents shall remain
unchanged and in full force and effect. No waiver by the Administrative Agent or
the Banks under the Loan Agreement or any other Loan Document is granted or
intended except as expressly set forth herein, and the Administrative Agent and
the Banks expressly reserve the right to require strict compliance in all other
respects (whether or not in connection with any Requests for Advance). Except as
set forth herein, the amendment agreed to herein shall not constitute a
modification of the Loan Agreement or any of the other Loan Documents, or a
course of dealing with the Administrative Agent and the Banks at variance with
the Loan Agreement or any of the other Loan Documents, such as to require
further notice by the Administrative Agent, the Banks or the Majority Banks to
require strict compliance with the terms of the Loan Agreement and the other
Loan Documents in the future.

     4.   Representations and Warranties.  The Borrower hereby represents
          ------------------------------
and warrants in favor of each of the Administrative Agent and each Bank that the
representations and warranties contained in Section 4.1 of the Loan Agreement
and contained in the other Loan Documents remain true and correct as of the date
hereof, both before and after giving effect to this Amendment, except to the
extent previously fulfilled in accordance with the terms of the Loan Agreement
or such other Loan Document, as applicable, or to the extent relating
specifically to the Agreement Date.  No Default now exists or will be caused
hereby.

     5.   Condition Precedent.  The effectiveness of this Amendment is
          -------------------
subject to the receipt by the Administrative Agent of counterparts hereof
executed by the Banks and the Borrower and of all documents, instruments,
consents or items which the Administrative Agent shall deem appropriate in
connection herewith.

     6.   Loan Documents.  This document shall be deemed to be a Loan
          --------------
Document for all purposes under the Loan Agreement and the other Loan Documents.

     7.   Counterparts.  This Amendment may be executed in any number of
          ------------
counterparts, each of which shall be deemed to be an original, but all such
separate counterparts shall together constitute but one and the same instrument.

     8.   Governing Law.  This Amendment shall be construed in accordance
          -------------
with and governed by the laws of the State of New York.

     9.   Severability.  Any provision of this Amendment which is
          ------------
prohibited or unenforceable shall be ineffective to the extent of such
prohibition or unenforceability without invalidating the remaining provisions
hereof in that jurisdiction or affecting the validity or enforceability of such
provision in any other jurisdiction.

                                      -4-
<PAGE>

     IN WITNESS WHEREOF, the parties hereto have executed this Amendment or
caused it to be executed by their duly authorized officers, all as of the day
and year first above written.


BORROWERS:               AMERICAN TOWER, L.P.

                         By ATC GP INC.


                         By:  /s/ Joseph Winn
                              ---------------------------------------

                              Title:   Chief Financial Officer
                                    ---------------------------------


                         AMERICAN TOWERS, INC.


                         By:  /s/ Joseph Winn
                              ---------------------------------------

                              Title:   Chief Financial Officer
                                    ---------------------------------



ADMINISTRATIVE AGENT
AND BANKS:               TORONTO DOMINION (TEXAS), INC., as Administrative Agent
                         for itself and the Banks and as a Bank


                         By:  /s/ Jeffery R. Lents
                              ---------------------------------------

                              Title:   Vice President
                                    ---------------------------------



                         BANK OF AMERICA NATIONAL TRUST AND SAVINGS ASSOCIATION,
                         as a Bank


                         By:  /s/ Anthony M. Cacheria
                              ---------------------------------------

                              Title:   Authorized Signatory
                                    ---------------------------------

<PAGE>

                         BANK OF MONTREAL, as a Bank


                         By:  /s/ Sarah Kim
                              ---------------------------------------

                              Title:   Director
                                    ---------------------------------



                         THE BANK OF NEW YORK, as a Bank


                         By:  /s/ Geoffrey C. Brooks
                              ---------------------------------------

                              Title:   Vice President
                                    ---------------------------------



                         THE BANK OF NOVA SCOTIA, as a Bank


                         By:  /s/ Paul A. Weissenberger
                              ---------------------------------------

                              Title:   Authorized Signatory
                                    ---------------------------------



                         BANK OF SCOTLAND, as a Bank


                         By:  /s/ Janet Taffe
                              ---------------------------------------

                              Title:   Assistant Vice President
                                    ---------------------------------



                         BANKBOSTON, N.A., as a Bank


                         By:  /s/ Lenny Mason
                              ---------------------------------------

                              Title:   Director
                                    ---------------------------------

<PAGE>

                         BANKERS TRUST COMPANY, as a Bank


                         By:  /s/ Gregory Shefrin
                              ---------------------------------------

                              Title:   Principal
                                    ---------------------------------



                         BARCLAYS BANK, PLC, as a Bank


                         By:  /s/ Craig J. Lewis
                              ---------------------------------------

                              Title:   Director
                                    ---------------------------------



                         THE CHASE MANHATTAN BANK, as a Bank


                         By:  /s/ William E. Rottino
                              ---------------------------------------

                              Title:   Vice President
                                    ---------------------------------



                         THE CIT GROUP/EQUIPMENT FINANCING, INC., as a Bank


                         By:  /s/ J. E. Palmer
                              ---------------------------------------

                              Title:   Assistant Vice President
                                    ---------------------------------


                         CITY NATIONAL BANK, as a Bank


                         By:  /s/ David J. Allen
                              ---------------------------------------

                              Title:   Vice President
                                    ---------------------------------
<PAGE>

                         COBANK, ACB, as a Bank


                         By:  /s/ John Cole
                              ---------------------------------------

                              Title:   Vice President
                                    ---------------------------------


                         CREDIT LYONNAIS NEW YORK BRANCH, as a Bank


                         By:  /s/ Mark D. Thorsheim
                              ---------------------------------------

                              Title:   Vice President
                                    ---------------------------------


                         CREDIT SUISSE FIRST BOSTON, as a Bank


                         By:  /s/ Todd C. Morgan
                              ---------------------------------------

                              Title:   Director
                                    ---------------------------------


                         By:  /s/ Chris T. Horgan
                              ---------------------------------------

                              Title:   Vice President
                                    ---------------------------------


                         CRESTAR BANK, as a Bank


                         By:  /s/ Thomas Palmer
                              ---------------------------------------

                              Title:   Vice President
                                    ---------------------------------
<PAGE>

                         DRESDNER BANK AG, NEW YORK AND GRAND CAYMAN BRANCHES,
                         as a Bank


                         By:  /s/ Patrick A. Keleher
                              ---------------------------------------

                              Title:   Vice President
                                    ---------------------------------


                         By:  /s/ Brian E. Haughney
                              ---------------------------------------

                              Title:   Assistant Vice President
                                    ---------------------------------


                         FIRST NATIONAL BANK OF MARYLAND, as a Bank


                         By:  /s/ Christopher L. Smith
                              ---------------------------------------

                              Title:   Vice President
                                    ---------------------------------


                         FLEET NATIONAL BANK, as a Bank


                         By:  /s/ Amy B. Peden
                              ---------------------------------------

                              Title:   Assistant Vice President
                                    ---------------------------------


                         GENERAL ELECTRIC CAPITAL CORPORATION, as a Bank


                         By:  /s/ Mark F. Mylon
                              ---------------------------------------

                              Title:   Manager of Operations
                                    ---------------------------------
<PAGE>

                         THE HOWARD BANK, N.A., as a Bank


                         By:  /s/ Michael W. Quinn
                              ---------------------------------------

                              Title:   Senior Vice President
                                    ---------------------------------


                         KEY CORPORATE CAPITAL INC., as a Bank


                         By:  /s/ Kenneth J. Keeler
                              ---------------------------------------

                              Title:   Senior Vice President
                                    ---------------------------------


                         LEHMAN COMMERCIAL PAPER INC., as a Bank


                         By:  /s/ Michele Swanson
                              ---------------------------------------

                              Title:   Authorized Signatory
                                    ---------------------------------


                         MELLON BANK, N.A., as a Bank


                         By:  /s/ Henry S. Beukema
                              ---------------------------------------

                              Title:   Assistant Vice President
                                    ---------------------------------


                         MERCANTILE BANK NATIONAL ASSOCIATION, as a Bank


                         By:  /s/ John H. Phillips
                              ---------------------------------------

                              Title:   Vice President
                                    ---------------------------------
<PAGE>

                         THE MITSUBISHI TRUST AND BANKING CORPORATION, as a Bank


                         By:  /s/ Beatrice E. Kossodo
                              ---------------------------------------

                              Title:   Senior Vice President
                                    ---------------------------------


                         NATIONAL BANK OF CANADA, as a Bank


                         By:  /s/ Theresa White
                              ---------------------------------------

                              Title:   Vice President
                                    ---------------------------------


                         By:  /s/ James Drum
                              ---------------------------------------

                              Title:   Vice President
                                    ---------------------------------


                         PNC BANK, NATIONAL ASSOCIATION, as a Bank


                         By:  /s/ Kristen E. Talaber
                              ---------------------------------------

                              Title:   Vice President
                                    ---------------------------------


                         STATE STREET BANK AND TRUST COMPANY, as a Bank


                         By:  /s/ Edward C. Thaute
                              ---------------------------------------

                              Title:   Vice President
                                    ---------------------------------
<PAGE>

                         UNION BANK OF CALIFORNIA, N.A., as a Bank


                         By:  /s/ Stender E. Sweeney
                              ---------------------------------------

                              Title:   Assistant Vice President
                                    ---------------------------------


                         US TRUST, as a Bank


                         By:  /s/ Daniel G. Eastman
                              ---------------------------------------

                              Title:   Vice President
                                    ---------------------------------


                         WEBSTER BANK, as a Bank


                         By:
                              ---------------------------------------

                              Title:
                                    ---------------------------------

<PAGE>
                                                                    EXHIBIT 10.5
                                                                    ------------

                 FIFTH AMENDMENT TO FACILITY B LOAN AGREEMENT
                                  AND CONSENT


  THIS FIFTH AMENDMENT TO FACILITY B LOAN AGREEMENT AND CONSENT (this "Amendment
                                                                       ---------
and Consent"), dated as of the 29th day of September, 1999 (the "Amendment
- -----------                                                      ---------
Date"), by and among AMERICAN TOWER, L.P., a Delaware limited partnership, and
- ----
AMERICAN TOWERS, INC., a Delaware corporation (collectively, the "Borrower"),
                                                                  --------
the FINANCIAL INSTITUTIONS SIGNATORY HERETO and TORONTO DOMINION (TEXAS), INC.,
as administrative agent (the "Administrative Agent") for the Banks (as defined
                              --------------------
in the Loan Agreement defined below);

                              W I T N E S S E T H:
                              -------------------

  WHEREAS, the Borrower, the Banks and the Administrative Agent are parties to
that certain ATS Facility B Loan Agreement dated as of June 16, 1998, as amended
by that certain First Amendment to ATS Facility B Loan Agreement dated as of
October 30, 1998, that certain Second Amendment and Waiver to ATS Facility B
Loan Agreement dated as of February 8, 1999, that certain Third Amendment to ATS
Facility B Loan Agreement dated as of May 27, 1999 and that certain Fourth
Amendment to ATS Facility B Loan Agreement dated as of July 9, 1999 (as amended,
modified, supplemented and restated from time to time, the "Loan Agreement");
                                                            --------------
and

  WHEREAS, the Borrower has requested, and the Banks have agreed, on the terms
and subject to the conditions set forth herein, to permit the Parent (as defined
in the Loan Agreement) to incur certain indebtedness and to prepay the principal
amount of Indebtedness outstanding under the Parent Loan Agreement (as defined
in the Loan Agreement) and to make certain other amendments to the Loan
Agreement, in each case, as provided herein;

  NOW, THEREFORE, in consideration of the premises set forth above, the
covenants and agreements hereinafter set forth, and other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged, the
parties hereto agree that all capitalized terms used herein shall have the
meanings ascribed thereto in the Loan Agreement, and further agree as follows:

  1.      Amendment to Article 1.  Article 1 of the Loan Agreement,
          ----------------------
Definitions, is hereby amended by adding the following definition of
- -----------
"Convertible Notes," thereto in appropriate alphabetical order:
 -----------------

          "Convertible Notes" shall mean convertible notes issued by the Parent
           -----------------
  having the following terms: (a) such Convertible Notes shall be overfunded by
  an amount equal to all interest payable with respect thereto for the period
  commencing on the
<PAGE>

  date of issuance thereof through the second anniversary of the date of
  issuance, (b) no principal payments (other than in common stock of the Parent)
  on the Convertible Notes may be required until six (6) months after the
  Maturity Date, (c) the proceeds (other than any amount required to pay
  interest during any applicable overfunding period) of such Convertible Notes
  shall be contributed as equity to the Co-Borrowers to be applied to the Loans
  in accordance with the provisions of this Agreement with any remaining
  proceeds used to pay in full all outstanding amounts under the Parent Loan
  Agreement in accordance with that certain Fifth Amendment to Facility B Loan
  Agreement and Consent dated as of September 29, 1999, (d) not guaranteed by
  Subsidiaries of the Parent and (e) such Convertible Notes shall be unsecured
  and have such other terms and conditions substantially as set forth in the
  Offering Memorandum with respect thereto."

  2.      Amendment to Article 8. Section 8.1 of the Loan Agreement, Events of
          ----------------------                                     ---------
Default, is hereby amended by deleting subsection (q) thereof in its entirety
- -------
and by substituting the following in lieu thereof:

          "(q) The Parent shall incur or permit to remain outstanding any
  Indebtedness for Money Borrowed other than the Convertible Notes (or any
  refinancing of the foregoing which does not exceed the principal amount
  outstanding on the date of such refinancing); or"

  3.      Consent to Prepayment under Parent Loan Agreement.  This
          -------------------------------------------------
Amendment and Consent, when executed by the Majority Banks and accepted by the
Borrower, will, subject to the terms and conditions hereof, reflect the Banks'
consent to the prepayment by the Parent in full of all amounts outstanding under
the Parent Loan Agreement solely with a portion the proceeds of the Convertible
Notes remaining after application of such proceeds as required by Article 2 of
the Loan Agreement; provided, however, that prior to such prepayment, the Co-
                    -----------------
Borrowers apply the proceeds of the Convertible Notes (other than any amount
required to pay interest during any applicable overfunding period) as required
by Article 2 of the Loan Agreement.

  4.      No Other Amendment or Consent. Except for the amendments and consent
          -----------------------------
set forth above, the text of the Loan Agreement and all other Loan Documents
shall remain unchanged and in full force and effect. No waiver or consent by the
Administrative Agent or the Banks under the Loan Agreement or any other Loan
Document is granted or intended except as expressly set forth herein, and the
Administrative Agent and the Banks expressly reserve the right to require strict
compliance in all other respects (whether or not in connection with any Requests
for Advance). Except as set forth herein, the amendments and consent agreed to
herein shall not constitute a modification of the Loan Agreement or any of the
other Loan Documents, or a course of dealing with the Administrative Agent and
the

                                      -2-
<PAGE>

Banks at variance with the Loan Agreement or any of the other Loan Documents,
such as to require further notice by the Administrative Agent, the Banks or the
Majority Banks to require strict compliance with the terms of the Loan Agreement
and the other Loan Documents in the future.

  5.      Loan Documents. This Amendment and Consent shall be deemed to be a
          --------------
Loan Document for all purposes under the Loan Agreement and the other Loan
Documents.

  6.      Counterparts. This Amendment and Consent may be executed in any number
          ------------
of counterparts, each of which shall be deemed to be an original, but all such
separate counterparts shall together constitute but one and the same instrument.

  7.      Governing Law. This Amendment and Consent shall be construed in
          -------------
accordance with and governed by the laws of the State of New York.

  8.      Severability. Any provision of this Amendment and Consent which is
          ------------
prohibited or unenforceable shall be ineffective to the extent of such
prohibition or unenforceability without invalidating the remaining provisions
hereof in that jurisdiction or affecting the validity or enforceability of such
provision in any other jurisdiction.

             [THE REMAINDER OF THIS PAGE INTENTIONALLY LEFT BLANK]

                                      -3-
<PAGE>

  IN WITNESS WHEREOF, the parties hereto have executed this Amendment and
Consent or caused it to be executed by their duly authorized officers, all as of
the day and year first above written.


BORROWERS:               AMERICAN TOWER, L.P.

                         By ATC GP INC.



                         By:  /s/ Joseph L. Winn
                              ------------------------------------
                              Title:   Chief Financial Officer


                         AMERICAN TOWERS, INC.


                         By:  /s/ Joseph L. Winn
                              ------------------------------------
                              Title:   Chief Financial Officer


ADMINISTRATIVE AGENT
AND BANKS:               TORONTO DOMINION (TEXAS), INC., as Administrative Agent
                         for itself and the Banks and as a Bank


                              /s/ Jeffrey R. Lents
                              ------------------------------------
                              Title:   Vice President
<PAGE>

                         BANK OF AMERICA, N.A. (formerly known as Bank of
                         America National Trust and Savings Association), as a
                         Bank


                         By: /s/ Todd Shipley
                             ------------------------------------

                             Title: Senior Vice President
                                    ----------------------------


                         BANK OF MONTREAL, as a Bank


                         By: /s/ Sarah Kim
                             ------------------------------------

                             Title: Director
                                    ----------------------------


                         THE BANK OF NEW YORK, as a Bank


                         By: /s/ Geoffrey C. Brooks
                             ------------------------------------

                             Title: Vice President
                                    ----------------------------


                         THE BANK OF NOVA SCOTIA, as a Bank


                         By: /s/ Paul A. Weissenberger
                             ------------------------------------

                             Title: Authorized Signatory
                                    ----------------------------
<PAGE>

                         BANK OF SCOTLAND, as a Bank


                         By: /s/ Annie Glynn
                             ------------------------------------

                             Title: Senior Vice President
                                    ----------------------------


                         BANKBOSTON, N.A., as a Bank


                         By: /s/ Lenny Mason
                             ------------------------------------

                             Title: Director
                                    ----------------------------


                         BANKERS TRUST COMPANY, as a Bank


                         By: /s/ Gregory Shefrin
                             ------------------------------------

                             Title: Principal
                                    ----------------------------


                         BARCLAYS BANK, PLC, as a Bank


                         By: /s/ Craig J. Lewis
                             ------------------------------------

                              Title: Director
                                     ----------------------------


                         THE CHASE MANHATTAN BANK, as a Bank


                         By: /s/ William E. Rottino
                             ------------------------------------

                             Title: Vice President
                                    ----------------------------
<PAGE>

                         THE CIT GROUP/EQUIPMENT FINANCING, INC., as a Bank


                         By: /s/ Daniel E. A. Nichols
                             ------------------------------------

                              Title: Assistant Vice President
                                     ----------------------------


                         CITY NATIONAL BANK, as a Bank


                         By: /s/ Rod Bollins
                             ------------------------------------

                              Title: Vice President
                                     ----------------------------


                         COBANK, ACB, as a Bank


                         By: /s/ Teresa L. Fountain
                             ------------------------------------

                             Title: Assistant Corporate Secretary
                                    -----------------------------


                         CREDIT LYONNAIS NEW YORK BRANCH, as a Bank


                         By: /s/ Mark Campellone
                             ------------------------------------

                             Title: First Vice President
                                    ----------------------------
<PAGE>

                         CREDIT SUISSE FIRST BOSTON, as a Bank


                         By: /s/ Todd C. Morgan
                             ------------------------------------

                             Title: Director
                                    ----------------------------


                         By: /s/ Kristin Lepri
                             ------------------------------------

                             Title: Associate
                                    ----------------------------


                         CRESTAR BANK, as a Bank


                         By: /s/ Edwin D. Brooks, Jr.
                             ------------------------------------

                             Title: Executive Vice President
                                    ----------------------------


                         DRESDNER BANK AG, NEW YORK AND GRAND CAYMAN BRANCHES,
                         as a Bank


                         By: /s/ Constance Loosemore
                             ------------------------------------

                              Title: Assistant Vice President
                                     ----------------------------


                         By: /s/ Patrick A. Keleher
                             ------------------------------------

                             Title: Vice President
                                    ----------------------------
<PAGE>

                         ALLFIRST BANK, as a Bank


                         By: /s/ W. Blake Hampson
                             ------------------------------------

                             Title: Vice President
                                    ----------------------------


                         FLEET NATIONAL BANK, as a Bank


                         By: /s/ Jeffrey R. Greene
                             ------------------------------------

                              Title: Vice President
                                     ----------------------------


                         THE FUJI BANK, LIMITED, as a Bank


                         By: Kazuyuki Nishimura
                             ------------------------------------

                              Title: Senior Vice President and Group Head
                                     ------------------------------------


                         GENERAL ELECTRIC CAPITAL CORPORATION, as a Bank


                         By: /s/ Michael J. Tzougrakis
                             ------------------------------------

                              Title: Manager of Operations
                                     ----------------------------
<PAGE>

                         THE HOWARD BANK, N.A., as a Bank


                         By: /s/ Michael W. Quinn
                             ------------------------------------

                             Title: Senior Vice President
                                    ----------------------------


                         KEY CORPORATE CAPITAL INC., as a Bank


                         By: /s/ Jason R. Weaver
                             ------------------------------------

                             Title: Vice President
                                    ----------------------------


                         MELLON BANK, N.A., as a Bank

                         By: /s/ Henry Beukema
                             ------------------------------------

                             Title: Assistant Vice President
                                    ----------------------------






<PAGE>

                         MERCANTILE BANK NATIONAL ASSOCIATION, as a Bank


                         By: John H. Phillips
                             ------------------------------------

                              Title: Vice President
                                     ----------------------------


                         THE MITSUBISHI TRUST AND BANKING CORPORATION, as a Bank


                         By: /s/ Toshihiro Hayashi
                             ------------------------------------

                             Title: Senior Vice President
                                    ----------------------------


                         NATIONAL BANK OF CANADA, as a Bank


                         By: /s/ Theresa White
                             ------------------------------------

                             Title: Vice President
                                    ----------------------------


                         By: /s/ Vincent Lima
                             ------------------------------------

                              Title: Vice President
                                     ----------------------------


                         PNC BANK, NATIONAL ASSOCIATION, as a Bank


                         By: /s/ Kristen E. Talaber
                             ------------------------------------

                             Title: Vice President
                                    ----------------------------
<PAGE>

                         STATE STREET BANK AND TRUST COMPANY, as a Bank


                         By: /s/ Edward C. Thaute
                             ------------------------------------

                             Title: Vice President
                                    ----------------------------


                         UNION BANK OF CALIFORNIA, N.A., as a Bank


                         By: /s/ Darren H. Miyata
                             ------------------------------------

                              Title: Assistant Vice President
                                     ----------------------------


                         US TRUST, as a Bank


                         By: /s/ Daniel G. Eastman
                             ------------------------------------

                             Title: Vice President
                                    ----------------------------


                         WEBSTER BANK, as a Bank


                         By: /s/ Juliana B. Dalton
                             ------------------------------------

                             Title: Vice President
                                    ----------------------------

<PAGE>

                                                                    EXHIBIT 10.6
                                                                    ------------
                                FIRST AMENDMENT
                                      TO
                             PARENT LOAN AGREEMENT

     THIS FIRST AMENDMENT TO PARENT LOAN AGREEMENT (this "Amendment"), dated as
                                                          ---------
 of the 9th day of July, 1999 (the "Amendment Date"), by and among AMERICAN
                                    --------------
TOWER CORPORATION, a Delaware corporation (the "Borrower"), the FINANCIAL
                                                --------
INSTITUTIONS SIGNATORY HERETO and TORONTO DOMINION (TEXAS), INC., as
administrative agent (the "Administrative Agent") for the Lenders (as defined in
                           --------------------
the Loan Agreement defined below);


                              W I T N E S S E T H:
                              -------------------


     WHEREAS, the Borrower, the Lenders and the Administrative Agent are parties
to that certain Parent Loan Agreement dated as of June 16, 1998 (as amended,
modified, supplemented and restated from time to time, the "Loan Agreement");
                                                            --------------
and

     WHEREAS, the Borrower has requested, and the Lenders have agreed, on the
terms and subject to the conditions set forth herein, to make certain amendments
to the Loan Agreement as provided herein;

     NOW, THEREFORE, in consideration of the premises set forth above, the
covenants and agreements hereinafter set forth, and other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged, the
parties hereto agree that all capitalized terms used herein shall have the
meanings ascribed thereto in the Loan Agreement, and further agree as follows:

     1.  Amendments to Article 1.
         -----------------------

     (a)  Article 1 of the Loan Agreement, Definitions, is hereby amended by
                                           -----------
adding the following new definitions of "Broker/Dealer" and "communications
                                         -------------       --------------
site" thereto in appropriate alphabetical order:
- ----

     "'Broker/Dealer' shall mean, with respect to any Investment or Acquisition
      -------------
     permitted under Section 7.6(a) hereof, (a) any broker/dealer (acting as
     principal) registered as a broker or a dealer under Section 15 of the
     Exchange Act, the unsecured short-term debt obligations of which are rated
     "P-1" by Moody's Investors Service, Inc. and at least "A-1" by Standard and
     Poor's Ratings Group, a division of The McGraw-Hill Companies, Inc., at the
     time of entering into such Investment or Acquisition or (b) an unrated,
     broker/dealer, acting as principal, that is a wholly-owned Subsidiary of a
     non-bank or bank holding company, the unsecured short-term debt obligations
     of which are rated "P-1" by Moody's Investors Service, Inc. and at least
     "A-1" by Standard and Poor's Ratings
<PAGE>

     Group, a division of The McGraw-Hill Companies, Inc., at the time of
     entering into such Investment or Acquisition."

          "'communications site' shall mean (a) any undeveloped real property
           -------------------
     and (b) communication towers which have no bona fide customers on the date
     of acquisition thereof."

     (b)  Article 1 of the Loan Agreement, Definitions, is hereby amended by
deleting the definition of "Subsidiary" in its entirety and by substituting the
                            ----------
following in lieu thereof:

          "'Subsidiary' shall mean, as applied to any Person, (a) any
           ----------
     corporation of which no less than fifty percent (50%) of the outstanding
     stock (other than directors' qualifying shares) having ordinary voting
     power to elect a majority of its board of directors, regardless of the
     existence at the time of a right of the holders of any class or classes of
     securities of such corporation to exercise such voting power by reason of
     the happening of any contingency, or any partnership of which no less than
     fifty percent (50%) of the outstanding partnership interests, is at the
     time owned directly or indirectly by such Person, or by one or more
     Subsidiaries of such Person, or by such Person and one or more Subsidiaries
     of such Person, provided, however, that if such Person and/or such Person's
     Subsidiaries directly or indirectly own no more than fifty percent (50%) of
     such Subsidiary's ownership interests, then such Subsidiary's operating or
     governing documents must require (i) such Subsidiary's net cash after the
     establishment of reserves be distributed to its equity holders no less
     frequently than quarterly and (ii) the consent of such Person and/or such
     Person's Subsidiaries to amend or otherwise modify the provisions of such
     operating or governing documents requiring such distributions, or (b) any
     other entity which is directly or indirectly controlled or capable of being
     controlled by such Person, or by one or more Subsidiaries of such Person,
     or by such Person and one or more Subsidiaries of such Person."

     2.   Amendment to Article 7. Section 7.6 of the Loan Agreement, Investments
          ----------------------                                     -----------
and Acquisitions, is hereby amended by deleting subsections (a), (b) and (c)
- ----------------
thereof in their entirety and by substituting the following in lieu thereof:

          "(a)  the Borrower and any Restricted Subsidiary may directly or
     through a brokerage account or investment adviser (i) purchase marketable,
     direct obligations of the United States of America, its agencies and
     instrumentalities maturing within three hundred sixty-five (365) days of
     the date of purchase, (ii) purchase commercial paper, and other short-term
     obligations and business savings accounts issued by corporations, each of
     which shall have a combined net worth of at least $100,000,000 and each of
     which conducts a substantial part of its business in the United States of
     America, maturing within two hundred seventy (270) days from the date of
     the original issue thereof, and whose issuer is, at the time of purchase,
     rated "P-2" or better by Moody's Investors Service, Inc. or "A-2" or better
     by Standard and Poor's Ratings Group, a division of The McGraw-Hill
     Companies, Inc., (iii) purchase repurchase agreements,

                                      -2-
<PAGE>

     bankers' acceptances, and domestic and Eurodollar certificates of deposit
     maturing within three hundred sixty-five (365) days of the date of purchase
     which are issued by, or time deposits maintained with, (A) a United States
     national or state bank (or any domestic branch of a foreign bank) subject
     to supervision and examination by federal or state banking or depository
     institution authorities and having capital, surplus and undivided profits
     totaling more than $100,000,000 and rated "A" or better by Moody's
     Investors Service, Inc. or Standard and Poor's Ratings Group, a division of
     The McGraw-Hill Companies, Inc., or (B) a Broker/Dealer, and (iv) invest in
     money market funds having a rating from Moody's Investors Service, Inc. and
     Standard and Poor's Ratings Group, a division of The McGraw-Hill Companies,
     Inc., in the highest investment category granted thereby;

          (b) so long as no Default then exists or would be caused thereby, any
     Restricted Subsidiary may establish Unrestricted Subsidiaries and make
     Investments in such Unrestricted Subsidiaries of up to, in the aggregate,
     at any time, the sum of (i) $60,000,000, with loans borrowed under the ATS
     Facility A Loan Agreement or the ATS Facility B Loan Agreement, and (ii)
     and equity proceeds not used to pay the Separation Obligations or to make
     Investments permitted under Sections 7.6(c) and (d) hereof'

          (c) so long as no Default then exists or would be caused thereby, and
     subject to compliance with Section 5.12 hereof, any Restricted Subsidiary
     may make Acquisitions; provided, however, that Acquisitions described in
                            --------  -------
     clause (iii) of the definition of "Acquisitions" and Acquisitions of other
     services businesses, such as construction and teleport businesses, shall
     not exceed at any time, in the aggregate, the sum of (i) $50,000,000, and
     (ii) equity proceeds not used to pay the Separation Obligations after the
     Agreement Date or to make Investments permitted under Section 7.6(b) and
     (d) hereof;"

     3.   No Other Amendment or Waiver.  Except for the amendments set
          ----------------------------
forth above, the text of the Loan Agreement and all other Loan Documents shall
remain unchanged and in full force and effect.  No waiver by the Administrative
Agent or the Lenders under the Loan Agreement or any other Loan Document is
granted or intended except as expressly set forth herein, and the Administrative
Agent and the Lenders expressly reserve the right to require strict compliance
in all other respects (whether or not in connection with any Requests for
Advance).  Except as set forth herein, the amendment agreed to herein shall not
constitute a modification of the Loan Agreement or any of the other Loan
Documents, or a course of dealing with the Administrative Agent and the Lenders
at variance with the Loan Agreement or any of the other Loan Documents, such as
to require further notice by the Administrative Agent, the Lenders or the
Majority Lenders to require strict compliance with the terms of the Loan
Agreement and the other Loan Documents in the future.

     4.   Representations and Warranties.  The Borrower hereby represents
          ------------------------------
and warrants in favor of each of the Administrative Agent and each Lender that
the representations and

                                      -3-
<PAGE>

warranties contained in Section 4.1 of the Loan Agreement and contained in the
other Loan Documents remain true and correct as of the date hereof, both before
and after giving effect to this Amendment, except to the extent previously
fulfilled in accordance with the terms of the Loan Agreement or such other Loan
Document, as applicable, or to the extent relating specifically to the Agreement
Date. No Default now exists or will be caused hereby.

     5.   Condition Precedent.  The effectiveness of this Amendment is
          -------------------
subject to the receipt by the Administrative Agent of counterparts hereof
executed by the Lenders and the Borrower and of all documents, instruments,
consents or items which the Administrative Agent shall deem appropriate in
connection herewith.

     6.   Loan Documents.  This document shall be deemed to be a Loan
          --------------
Document for all purposes under the Loan Agreement and the other Loan Documents.

     7.   Counterparts.  This Amendment may be executed in any number of
          ------------
counterparts, each of which shall be deemed to be an original, but all such
separate counterparts shall together constitute but one and the same instrument.

     8.   Governing Law.  This Amendment shall be construed in accordance
          -------------
with and governed by the laws of the State of New York.

     9.   Severability.  Any provision of this Amendment which is prohibited or
          ------------
unenforceable shall be ineffective to the extent of such prohibition or
unenforceability without invalidating the remaining provisions hereof in that
jurisdiction or affecting the validity or enforceability of such provision in
any other jurisdiction.

             [THE REMAINDER OF THIS PAGE INTENTIONALLY LEFT BLANK]

                                      -4-
<PAGE>

     IN WITNESS WHEREOF, the parties hereto have executed this Agreement or
caused it to be executed by their duly authorized officers, all as of the day
and year first above written.


BORROWER:                          AMERICAN TOWER CORPORATION


                                   By:  /s/ Joseph Winn
                                      ------------------------------------------

                                   Title:   Chief Financial Officer
                                         ---------------------------------------


ADMINISTRATIVE AGENT
AND LENDERS:                       TORONTO DOMINION (TEXAS), INC., as
                                   Administrative Agent for itself and for the
                                   Lenders and as a Lender

                                   By:  /s/ Jeffery R. Lents
                                      ------------------------------------------

                                   Title:   Vice President
                                         ---------------------------------------


                                   ARCHIMEDES FUNDING II, LTD, as a Lender
                                   By: ING Capital Advisors, LLC, as Collateral
                                   Manager

                                   By:  /s/ Helen Y. Rhee
                                      ------------------------------------------

                                   Title:   Vice President and Portfolio Manager
                                         ---------------------------------------


                                   DEBT STRATEGIES FUND, INC., as a Lender


                                   By:  /s/ Joseph P. Matteo
                                      ------------------------------------------

                                   Title:   Authorized Signatory
                                         ---------------------------------------

<PAGE>

                                   DEBT STRATEGIES FUND II, INC., as a Lender


                                   By:  /s/ Joseph P. Matteo
                                      ------------------------------------------

                                   Title:   Authorized Signatory
                                         ---------------------------------------


                                   FC CBO II LIMITED, as a Lender


                                   By:  /s/ Mike McCarthy
                                      ------------------------------------------

                                   Title:   Collateral Manager
                                         ---------------------------------------


                                   FIRST DOMINION FUNDING I, as a Lender


                                   By:  /s/ Andrew H. Marshak
                                      ------------------------------------------

                                   Title:   Authorized Signatory
                                         ---------------------------------------


                                   FIRST DOMINION FUNDING II, as a Lender


                                   By:  /s/ Andrew H. Marshak
                                      ------------------------------------------

                                   Title:   Authorized Signatory
                                         ---------------------------------------


                                   FRANKLIN FLOATING RATE TRUST, as a Lender


                                   By:  /s/ Chauncey Lufkin
                                      ------------------------------------------

                                   Title:   Vice President
                                         ---------------------------------------
<PAGE>

                                   GENERAL ELECTRIC CAPITAL CORPORATION, as a
                                   Lender

                                   By:  /s/ Mark F. Mylon
                                      ------------------------------------------

                                   Title:   Manager-Operations
                                         ---------------------------------------


                                   ING HIGH INCOME PRINCIPAL PRESERVATION FUND
                                   HOLDINGS, LDC
                                   By: ING Capital Advisors, Inc., as Investment
                                   Advisors, Inc., as a Lender

                                   By:  /s/ Helen Y. Rhee
                                      ------------------------------------------

                                   Title:   Vice President and Portfolio Manager
                                         ---------------------------------------


                                   KZH SHOSHONE LLC, as a Lender


                                   By:  /s/ Virginia Conway
                                      ------------------------------------------

                                   Title:   Authorized Agent
                                         ---------------------------------------


                                   MERRILL LYNCH GLOBAL INVESTMENT SERIES INCOME
                                   STRATEGIES PORTFOLIO, as a Lender
                                   By:  Merrill Lynch Asset Management, L.P., as
                                   Investment Advisor


                                   By:  /s/ Joseph P. Matteo
                                      ------------------------------------------

                                   Title:   Authorized Signatory
                                         ---------------------------------------

<PAGE>

                                   OCTAGON INVESTMENT PARTNERS II, LLC, as a
                                   Lender
                                   By: Octagon Credit Investors, LLC, as Sub
                                   Investment Managers

                                   By:  /s/ Andrew D. Gordon
                                      ------------------------------------------

                                   Title:   Portfolio Manager
                                         ---------------------------------------


                                   OCTAGON LOAN TRUST, as a Lender
                                   By: Octagon Credit Investors, LLC, as Manager


                                   By:  /s/ Andrew D. Gordon
                                      ------------------------------------------

                                   Title:   Managing Director
                                         ---------------------------------------


                                   SANKATY HIGH YIELD ASSET PARTNERS, L.P., as a
                                   Lender

                                   By:  /s/ Diane J. Exter
                                      ------------------------------------------

                                   Title:   Portfolio Manager
                                         ---------------------------------------



                                   SENIOR HIGH INCOME PORTFOLIO, INC., as a
                                   Lender

                                   By:  /s/ Joseph P. Matteo
                                      ------------------------------------------

                                   Title:   Authorized Signatory
                                         ---------------------------------------



                                   UNION BANK OF CALIFORNIA, N.A., as a Lender


                                   By:  /s/ Stender E. Sweeney
                                      ------------------------------------------

                                   Title:   Assistant Vice President
                                         ---------------------------------------

<TABLE> <S> <C>

<PAGE>
<ARTICLE> 5
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM THE AMERICAN
TOWE CORPORATION AND SUBSIDIARIES SEPTEMBER 30, 1999 CONDENSED CONSOLIDATED
FINANCIAL STATEMENTS AND IS QUALIFIED IN ITS ENTIRETY BY REFERNCE TO SUCH
CONDENSED CONSOLIDATED FINANCIAL STATEMENTS.
</LEGEND>
<MULTIPLIER> 1,000

<S>                             <C>
<PERIOD-TYPE>                   9-MOS
<FISCAL-YEAR-END>                          DEC-31-1999
<PERIOD-START>                             JAN-01-1999
<PERIOD-END>                               SEP-30-1999
<CASH>                                          41,711
<SECURITIES>                                         0
<RECEIVABLES>                                   41,126
<ALLOWANCES>                                   (2,308)
<INVENTORY>                                      7,123
<CURRENT-ASSETS>                               119,539
<PP&E>                                         948,821
<DEPRECIATION>                                (56,576)
<TOTAL-ASSETS>                               2,620,558
<CURRENT-LIABILITIES>                           77,559
<BONDS>                                        378,640
                                0
                                          0
<COMMON>                                         1,557
<OTHER-SE>                                   2,156,177
<TOTAL-LIABILITY-AND-EQUITY>                 2,620,558
<SALES>                                              0
<TOTAL-REVENUES>                               169,100
<CGS>                                                0
<TOTAL-COSTS>                                  198,839
<OTHER-EXPENSES>                                     0
<LOSS-PROVISION>                                     0
<INTEREST-EXPENSE>                              17,497
<INCOME-PRETAX>                               (33,416)
<INCOME-TAX>                                       942
<INCOME-CONTINUING>                           (32,474)
<DISCONTINUED>                                       0
<EXTRAORDINARY>                                      0
<CHANGES>                                            0
<NET-INCOME>                                  (32,474)
<EPS-BASIC>                                      (.22)
<EPS-DILUTED>                                    (.22)


</TABLE>


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