<PAGE>

                                                                    Exhibit 10.8

                            INTERMEDIARY AGREEMENT

  This Intermediary Agreement (the "Agreement"), made as of the _____day of
______, 2000, among AT&T Wireless PCS, LLC, a Delaware limited liability company
("AT&T"), TeleCorp PCS, Inc., a Delaware corporation ("TeleCorp"), TeleCorp PCS,
LLC, a Delaware limited liability company ("TeleCorp LLC"), TeleCorp Holding
Corp, Inc., a Delaware corporation ("TeleCorp Holding"), TeleCorp
Communications, Inc., a Delaware corporation ("TeleCorp Communications"),
TeleCorp Equipment Leasing, L.P., a Delaware limited partnership ("TeleCorp
Equipment"), TeleCorp Realty, LLC, a Delaware limited liability company
("TeleCorp Realty") (TeleCorp, TeleCorp LLC, TeleCorp Holding, TeleCorp
Communications, TeleCorp Equipment, and TeleCorp Realty hereinafter
collectively, the "TeleCorp Affiliates") and _______________________________, a
_______________________________ ("Intermediary").  Capitalized terms used but
not otherwise defined herein shall have the meanings assigned to such terms in
the Asset Exchange Agreement (the "Asset Exchange Agreement") among AT&T and the
TeleCorp Affiliates, dated as of February 28, 2000.

                                  WITNESSETH:

WHEREAS, AT&T and the TeleCorp Affiliates have entered into the Asset Exchange
Agreement and this form of  Agreement is an Exhibit to the Asset Exchange
Agreement;

WHEREAS, pursuant to the Asset Exchange Agreement, AT&T desires to exchange the
AT&T Assets for the Boston Licenses and the TeleCorp Affiliates desire to
exchange the Boston Licenses for the AT&T Assets;

WHEREAS, in connection with the exchange of the Boston Licenses for the AT&T
Assets, certain payments of  Cash Consideration are required, and certain
deliveries of Stock Consideration may be required, and in connection with the
transfer of the Boston Business, an Asset Payment is required;

WHEREAS, AT&T and the TeleCorp Affiliates wish to retain the Intermediary for
purposes of:

  (i)   consummating the transactions contemplated by each of the Acquisition
        Agreements in accordance with the provisions of each such agreement;

  (ii)  delivering to each of the counterparties to each of the Acquisition
        Agreements that portion of the Cash Consideration as is allocable to the
        purchase price required to be paid under the Acquisition Agreements and
        such instruments, certificates, opinions and other agreements as may be
        required pursuant to the terms of each of the Acquisition Agreements to
        consummate the transactions contemplated by each of such agreements;

  (iii) directing that such counterparties deliver any and all rights to, and/or
        assign, as applicable, all of the Polycell Licenses and the ABC Licenses
        and execute and deliver such instruments, certificates, opinions and
        other agreements as may be required pursuant to the terms of each of the
        Acquisition Agreements to consummate the transactions contemplated by
        each of the Acquisition Agreements to TeleCorp or another Designated
        TeleCorp Affiliate as applicable;

  (iv)  delivering to Polycell Communications, Inc. the required Stock
        Consideration, if any;

  (v)   delivering the TeleCorp Assignments to AT&T, as applicable; and

  (vi)  delivering the AT&T Assignments and Asset Payment to the Designated
        TeleCorp Affiliates, as applicable.

WHEREAS, TeleCorp will act as agent for the TeleCorp Affiliates for purposes of
effecting the transactions contemplated hereunder; and
<PAGE>

WHEREAS, it is the intention of the parties that (i) the Intermediary constitute
a "qualified intermediary" within the meaning of U.S. Treasury Regulations
("Regulations") section 1.1031(k)-1(g)(4)(iii), (ii) the transactions
contemplated by this Agreement qualify for the safe harbor provided in
Regulations section 1.1031(k)-1(g)(4), and (iii) the exchange of the AT&T Assets
for the Boston Licenses by AT&T on the one hand and the TeleCorp Affiliates on
the other, as specified in Schedule 1.3 of the Asset Exchange Agreement attached
herewith as Attachment A, shall to the greatest extent possible, qualify as an
exchange within the meaning of section 1031 of the Code and the Regulations
issued thereunder, and that this Agreement be so construed.

NOW, THEREFORE, in consideration of the mutual promises herein contained, AT&T,
the TeleCorp Affiliates, and Intermediary agree as follows:

                                     FIRST

  A.  On the Closing Date, AT&T shall (i) execute and deliver to the
Intermediary (A) assignments of the rights to direct the transfer to TeleCorp
Holding of (I) all rights to the AT&T Acquired Assets and (II) the other rights
and obligations of the Polycell Buyer and AT&T under the Polycell Acquisition
Agreement and the ABC Acquisition Agreement, respectively, (B) license
assignments to TeleCorp LLC of all of AT&T's rights to the AT&T Owned Assets,
(ii) deliver or cause to be delivered to the Intermediary the Cash Consideration
and the Asset Payment, and (iii) direct the Intermediary to take all actions
necessary to (A) consummate all of the transactions contemplated by the
Acquisition Agreements, including without limitation payment of the Cash
Consideration and the Stock Consideration, if any, to the respective recipients
thereof, (B) cause the AT&T Acquired Assets to be transferred to TeleCorp
Holding, (C) assign and transfer to TeleCorp all other rights and obligations
under the Acquisition Agreements, (D) cause the AT&T Owned Assets to be
transferred to TeleCorp LLC and (E) pay the Asset Payment to the Designated
TeleCorp Affiliates.

  B.  The TeleCorp Affiliates shall (i) execute and deliver, or cause to be
executed and delivered, to the Intermediary a bill of sale and an assignment and
assumption agreement of all of its and any other Designated TeleCorp Affiliate's
rights to the TeleCorp Assets, (ii) deliver the Stock Consideration, if any, and
(iii) direct the Intermediary to cause all rights to the TeleCorp Assets to be
transferred, as applicable, to AT&T.

  C.  The parties hereto intend that the Intermediary shall be considered to
have "acquired" the AT&T Assets and the TeleCorp Assets, consistent with
Regulations section 1.1031(k)-1(g)(4), through the assignment of rights as
provided in this Article FIRST, and this Article FIRST shall be so construed.

                                    SECOND

  A.  On the Closing Date or on the first practicable date thereafter that is no
later than the earlier of (1) 180 days after the Closing Date, and (2) the first
due date of the federal income tax return of any TeleCorp Affiliate for the year
in which the Closing Date occurs, determined with regard to extensions,
Intermediary shall deliver to the TeleCorp Affiliates specified in Attachment A
the AT&T Assets, and to TeleCorp the Asset Payment pursuant to the Asset
Exchange Agreement, together with any interest thereon, provided, however, that
any such interest shall not be delivered prior to the receipt by the TeleCorp
Affiliate of all of the AT&T Assets.

  B.  On the Closing Date or on the first practicable date thereafter that is no
later than the earlier of (1) 180 days after the Closing Date and (2) the due
date of the federal income tax return of AT&T for the year in which the Closing
Date occurs, determined with regard to extensions, Intermediary shall deliver
the TeleCorp Assets to AT&T as specified in Attachment A and deliver the
required Stock Consideration (if any) to Polycell Communications Inc. pursuant
to section 2.2(f) of the Asset Exchange Agreement.

  C.  On the Closing Date or on the first practicable date thereafter that is no
later than the earlier of (1) 180 days after the Closing Date, and (2) the first
due date of the federal income tax return of any TeleCorp Affiliate for the year
in which the Closing Date occurs, determined with regard to extensions,
Intermediary shall deliver the Cash Consideration to the counterparties to the
Acquisition Agreements as attached to the Asset Exchange Agreement and shall
execute and deliver all documents necessary to consummate each of the
Acquisition Agreements.

                                      -2-
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  D.  Intermediary shall use its best efforts to effect the transactions, within
the time periods, contemplated by this Article SECOND.

                                     THIRD

  A.  Consummation of the transactions provided herein shall take place at the
office of Cadwalader, Wickersham & Taft, 100 Maiden Lane, New York, New York
10038 or at such other place as AT&T and the TeleCorp Affiliates may designate
by notice to Intermediary.

                                    FOURTH

  In the event that any of the AT&T Assets or TeleCorp Assets are transferred to
their respective owners subsequent to the Closing Date, the following provisions
shall apply, notwithstanding any provisions of this Agreement to the contrary:

  A.  The TeleCorp Affiliates have identified AT&T Assets, for the purposes of
Regulations section 1.1031(k)-1(c)(2) substantially in the form of Attachment B.

      (1)  In the event that AT&T is unable to deliver, or cause the delivery
of, any of the Polycell Licenses and ABC Licenses within 35 days after any of
TeleCorp and its Affiliates are treated as transferring any TeleCorp Asset
within the meaning of Regulation section 1.1031(k)-1(b)(2)(i) (the "First
Transfer Date"), then (a) within 45 days after the First Transfer Date, AT&T
shall deliver, or cause to be delivered, to the Intermediary, for delivery to
the Designated TeleCorp Affiliates, one of the following (chosen at AT&T's
option) which delivery will constitute full and complete satisfaction of AT&T's
obligations with respect to the Polycell Licenses or the ABC Licenses, as the
case may be: (A) cash in an amount equal to (1) $133 times the number of POPS
covered by the Polycell Licenses or the ABC Licenses, as the case may be, less
(2) the amount of the purchase price that was required to be paid pursuant to
the Polycell Acquisition Agreement or the ABC Acquisition Agreement, as the case
may be, and the transactions contemplated thereby; (B) an amount of Class A
Common Stock of TeleCorp having a value equal to the cash payable under clause
(A) above, valued based on the average of the closing prices of such stock for
the ten trading days immediately preceding the date of Closing; or (C) executed
assignments in form and substance satisfactory to TeleCorp for PCS licenses held
by AT&T and/or its Affiliates in the Jacksonville MTA and its surrounding BTAs
(the "Replacement Assets") (chosen at AT&T's option from among the Replacement
Assets) for at least an equivalent number of POPs, which shall be exchanged in
accordance with Article SECOND above.

      (2)  If AT&T chooses to comply with clause (C) above, TeleCorp will (A)
have the right to deliver to Intermediary a signed schedule substantially in the
form of Attachment B which identifies the property in clause (C) above
designating such Replacement Assets as "replacement assets" within the meaning
of Regulations section 1.1031(k)-l(c)(2), as well as to which entity such
property is to be transferred and (B) deliver to the Intermediary, and shall
cause the Intermediary to deliver to AT&T, an amount of Class A Common Stock of
TeleCorp, valued as set forth in paragraph (1) above, equal to the amount of the
purchase price that was required to be paid pursuant to the Polycell Acquisition
Agreement or the ABC Acquisition Agreement, as the case may be, and the
transactions contemplated thereby, and, if the number of POPs included in the
Replacement Assets chosen exceeds the number of POPs covered by the Polycell
Licenses or the ABC Licenses, as the case may be, TeleCorp will deliver to the
Intermediary and shall cause the Intermediary to deliver to AT&T an additional
amount of Class A Common Stock, valued as set forth in paragraph (1) above,
equal to $133 times the number of such excess POPs.

      (3)  AT&T shall cause the Intermediary to deliver all Replacement Assets
to the appropriate TeleCorp Affiliate pursuant to Article SECOND section D
above.

  B.  AT&T has identified the TeleCorp Assets, for purposes of Regulations
section 1.1031(k)-1(c)(2), substantially in the form of Attachment C. In the
event TeleCorp LLC is unable to deliver the TeleCorp Assets, or if the Asset
Exchange Agreement terminates prior to delivery of the TeleCorp Assets, and
prior to termination any TeleCorp Affiliate has acquired any of the AT&T
Acquired Assets pursuant to the Asset Exchange Agreement, then promptly upon
termination of the Asset Exchange Agreement, TeleCorp shall, as directed by
AT&T, either (A) sell

                                      -3-
<PAGE>

the Polycell Licenses or the ABC Licenses, as the case may be, to an entity
designated by AT&T, for a purchase price and otherwise on the same terms and
conditions as TeleCorp's acquisition of the Polycell Licenses or the ABC
Licenses or (B) issue to AT&T an amount of Class A Common Stock of TeleCorp
having a value equal to (1) $133 times the number of POPs covered by the
Polycell Licenses or the ABC Licenses, as the case may be, less (2) the amount
of the purchase price that was required to be paid, pursuant to the Polycell
Acquisition Agreement or the ABC Acquisition Agreement, as the case may be, and
the transactions contemplated thereby, such stock to be valued based on the
average of the closing prices of such stock for the ten trading days immediately
preceding the date of Closing.

  C.  (1)  On the Closing Date, Intermediary shall deposit into a segregated
account with _______________ an amount equal to the Cash Consideration and Asset
Payment (such deposit hereinafter referred to as the "Initial Exchange
Account").  The Initial Exchange Account shall be invested and reinvested in (i)
direct obligations of the United States of America, including money market
funds, (ii) obligations for which the full faith and credit of the United States
of America is pledged to provide for the payment of principal and interest,
(iii) commercial paper rated of the highest quality of Moody's Investors
Services, Inc. or Standard and Poor's Corporation, or (iv) certificates of
deposits with a maturity not greater than ___ days issued by a commercial bank
or banks having at least $1,000,000,000 in assets.  The Initial Exchange
Account, together with accumulated income therefrom, shall constitute the
"Exchange Account."

      (2)  Intermediary shall be entitled to withdraw funds from the Exchange
Account in order to make payments in accordance with the Asset Payment and the
Cash Consideration. The amount of the Exchange Account shall be reduced by the
amount of any withdrawals made by the Intermediary under this Section.

                                     FIFTH

  A.  None of AT&T and the TeleCorp Affiliates shall have any rights with
respect to any money or property held by Intermediary pursuant to this
Agreement, except to the extent expressly provided herein, or otherwise
permitted under Regulations section 1.1031(k)-1(g)(6).

  B.  The TeleCorp Affiliates and AT&T shall hold Intermediary harmless from and
indemnify Intermediary against, any and all claims (and expenses incurred
relating thereto) made against Intermediary at any time with respect to the AT&T
Assets, TeleCorp Assets, or any of the transactions contemplated by this
Agreement, except for any claims and expenses relating thereto arising from
Intermediary's gross negligence, bad faith or willful misconduct.  This
indemnity shall survive the Closing Date.

  C.  The TeleCorp Affiliates hereby appoint TeleCorp as their agent for the
transactions contemplated hereby.

                                     SIXTH

  Any notice, designation, consent, approval or other communication required or
permitted to be given pursuant to the provisions of this agreement (referred to,
collectively, as "Notice") shall, except as otherwise expressly provided herein,
be given in writing and shall be sent by certified or registered mail, Federal
Express or overnight courier addressed as follows:

If to AT&T:

AT&T Corp.                                          Telephone:
295 North Maple Avenue                              Telecopier: (908) 221-6618
Basking Ridge, NJ 07920

                                      -4-
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With a copy to:

Wachtell, Lipton, Rosen & Katz                      Telephone: (212) 403-1000
51 West 52/nd/ Street                               Telecopier: (212) 403-2000
New York, NY 10019
Attention: Steven A. Rosenblum and
           Trevor S. Norwitz

Friedman Kaplan & Seiler LLP                        Telephone:
875 Third Avenue                                    Telecopier: (212) 355-6401
New York, NY 10022
Attention: Gary D. Friedman

If to the TeleCorp Affiliates:

1010 North Glebe Road                               Telephone:
Suite 800                                           Telecopier: (703) 236-
Arlington, VA 22201
Attention: Thomas H. Sullivan

With a copy to:

Mintz, Levin, Cohn, Ferris, Glovsky and             Telephone:
Popeo, P.C.
One Financial Center                                Telecopier: (617) 542-2241
Boston, MA 02111
Attention: Alicia M.V. Wyman

Cadwalader, Wickersham & Taft
100 Maiden Lane                                     Telephone:
New York, NY 10038                                  Telecopier: (212) 504-6666
Attention: Brian Hoffman

If to Intermediary:                                 Telephone:__________________

_____________________________                       Telecopier:_________________

_____________________________

_____________________________

With a copy to:

_____________________________                       Telephone:__________________

_____________________________                       Telecopier:_________________

_____________________________

Any party may, by Notice given in accordance with the provisions of this
Article, designate any further or different address to which subsequent Notices
shall be sent pursuant to the provisions of this agreement. Any Notice shall be
deemed to have been given on the date such Notice shall have been delivered. If
such delivery shall be made on a Saturday, Sunday or holiday, said Notice shall
be deemed to have been given on the next succeeding business day, except for
Notices or identifications required only because of Article FOURTH.

                                      -5-
<PAGE>

                                    SEVENTH

  This Agreement shall be binding upon and shall inure to the benefit of the
parties hereto and their respective heirs, executors, administrators,
successors, and except as otherwise herein provided, their assigns. It is
understood and agreed that all understandings and agreements, other than the
Asset Exchange Agreement, heretofore had between the parties hereto are merged
in this agreement, which (together with the Asset Exchange Agreement) fully and
completely expresses their understanding. This Agreement may not be changed or
terminated orally, but only by an instrument in writing executed by the parties
hereto. This Agreement shall not be transferred or assigned without the prior
written consent of the parties hereto.

                                    EIGHTH

  THIS AGREEMENT SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS
OF THE STATE OF NEW YORK WITHOUT GIVING EFFECT TO THE CONFLICT OF LAW PRINCIPLES
THEREOF.

                                     NINTH

  AT&T hereby certifies under penalties of perjury that it is not a "foreign
person" as defined by Section 1445 of the Code and the regulations promulgated
thereunder, and that it is not subject to backup withholding. AT&T hereby
certifies under penalties of perjury that its United States taxpayer
identification number and address is true and correct as represented in
Attachment D.

  Each of the TeleCorp Affiliates hereby certify under penalties of perjury that
it is not a "foreign person" as defined by section 1445 of the Code and the
Regulations promulgated thereunder, and that it is not subject to backup
withholding.  Each of the TeleCorp Affiliates hereby certify under penalties of
perjury that its United States taxpayer identification number and address is
true and correct as represented in Attachment E.

                                    TENTH

  Each TeleCorp Affiliate and AT&T represents, warrants, and covenants that, and
Intermediary represents, warrants and covenants that, to the best of its
knowledge, Intermediary, (1) is not acting, and will not act, for or on behalf
of, or as the agent of, AT&T or TeleCorp Affiliate, in any capacity, before all
transactions contemplated hereunder are consummated, except as permitted under
Regulations section 1.1031-1(k)(2), (2) is not and will not be related to any
TeleCorp Affiliate or AT&T (or any agent thereof) within the meaning of
Regulations section 1.1031(k)-1(k)(3) or (4), and (3) is not and will not
otherwise be a disqualified person with respect to any TeleCorp Affiliate or
AT&T within the meaning of Regulations section 1.1031(k)-1(k).

                                   ELEVENTH

  Intermediary shall receive the sum of $__________ for acting as Intermediary
hereunder and for all services rendered in connection therewith.

IN WITNESS WHEREOF, the parties hereto set their hand and seals on the day and
year first above written.

  AT&T Wireless PCS, LLC:
  ----------------------

  ______________________

  ______________________

  Intermediary:
  ------------

                                      -6-
<PAGE>

  ______________________

  ______________________

  TeleCorp PCS, Inc.:
  ------------------

  ______________________

  ______________________

  TeleCorp PCS, LLC:
  -----------------

  ______________________

  ______________________

  TeleCorp Holding Corp, Inc.:
  ---------------------------

  ______________________

  ______________________

  TeleCorp Communications, Inc.:
  -----------------------------

  ______________________

  ______________________

  TeleCorp Equipment Leasing, L.P.:
  ---------------------------------

  ______________________

  ______________________

  TeleCorp Realty, LLC:
  --------------------

  ______________________

  ______________________

                                      -7-
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                                 ATTACHMENT A
                                 ------------
                                      TO
                                      --
                            INTERMEDIARY AGREEMENT
                            ----------------------

          [ATTACHMENT WILL MIRROR SCHEDULE 1.3 TO EXCHANGE AGREEMENT]

                                      -8-
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                                 ATTACHMENT B
                                 ------------
                                      TO
                                      --
                            INTERMEDIARY AGREEMENT
                            ----------------------

                      IDENTIFICATION OF EXCHANGE PROPERTY


                                     Under

                  Internal Revenue Code Section 1031(a)(3)(A)


ATTN: ________                                    DATE: ________

Gentlemen:

  Reference is made to that certain Intermediary Agreement dated __________
("the Agreement") between AT&T Wireless PCS, LLC, TeleCorp PCS, Inc., TeleCorp
PCS, LLC, TeleCorp Holding Corp, Inc., TeleCorp Communications, Inc., TeleCorp
Equipment Leasing, L.P., TeleCorp Realty, LLC (hereinafter collectively, the
"TeleCorp Affiliates") and __________ ("Intermediary").

  In accordance with Article Fourth of the Agreement, the TeleCorp Affiliates
hereby identify __________, __________ as Replacement Property under the
Agreement.  The legal description of the Replacement Property is attached.

  In accordance with Article Fourth of the Agreement, the TeleCorp Affiliates
hereby notify Intermediary of its acceptance of the above described Replacement
Property and request that Intermediary use its best efforts to acquire the
Replacement Property in accordance with the provisions of the Agreement.

  Please acknowledge receipt of the letter by signing below in the space
indicated, and return the original to the above address, Attn: ______________.
We will then send you a fully executed copy.


                                        _______________________________________
                                        [TeleCorp Affiliates]

Receipt Acknowledged:


_____________________________

_______________ Exchange Corporation

                                      -9-
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                                 ATTACHMENT C
                                 ------------
                                      TO
                                      --
                            INTERMEDIARY AGREEMENT
                            ----------------------

                      IDENTIFICATION OF EXCHANGE PROPERTY


                                     Under

                  Internal Revenue Code Section 1031(a)(3)(A)


ATTN: ________                                    DATE: ________

Gentlemen:

  Reference is made to that certain Intermediary Agreement dated __________
("the Agreement") between AT&T Wireless PCS, LLC, TeleCorp PCS, Inc., TeleCorp
PCS, LLC, TeleCorp Holding Corp, Inc., TeleCorp Communications, Inc., TeleCorp
Equipment Leasing, L.P., TeleCorp Realty, LLC (hereinafter collectively, the
"TeleCorp Affiliates") and __________ ("Intermediary").

  In accordance with Article Fourth of the Agreement, AT&T hereby identifies
__________, __________ as Replacement Property under the Agreement. The legal
description of the Replacement Property is attached.

  In accordance with Article Fourth of the Agreement, AT&T hereby notifies
Intermediary of its acceptance of the above described Replacement Property and
requests that Intermediary use its best efforts to acquire the Replacement
Property in accordance with the provisions of the Agreement.

  Please acknowledge receipt of the letter by signing below in the space
indicated, and return the original to the above address, Attn: ______________.
We will then send you a fully executed copy.


                                             ___________________________________
                                             [AT&T]

Receipt Acknowledged:


____________________________

_______________ Exchange Corporation

                                      -10-
<PAGE>

                                 ATTACHMENT D
                                 ------------
                                      TO
                                      --
                            INTERMEDIARY AGREEMENT
                            ----------------------



     [CERTIFICATION BY AT&T OF TAXPAYER IDENTIFICATION NUMBER AND ADDRESS]

                                      -11-
<PAGE>

                                 ATTACHMENT E
                                 ------------
                                      TO
                                      --
                            INTERMEDIARY AGREEMENT
                            ----------------------



  [CERTIFICATION BY TELECORP AFFILIATES OF TAXPAYER IDENTIFICATION NUMBER AND
                                   ADDRESS]

                                      -12-