<PAGE>


                                                                   Exhibit 10.21

                    ROAMING ADMINISTRATION SERVICE AGREEMENT

         ROAMING ADMINISTRATION SERVICE AGREEMENT ("Agreement") made this
_________________, 2000, by and between AT&T Wireless Services, Inc. ("AWS"), a
Delaware corporation, with its principal place of business at 5000 Carillon
Point, Kirkland, WA 98033, and Holding Company ("Holding Company"), a Delaware
corporation, with its principal place of business at 1010 N. Glebe Road,
Arlington, VA 22201.

                                    Recitals
                                    --------

         WHEREAS, Holding Company and its Affiliates (collectively, the
"Company") would like to receive certain benefits under Intercarrier Roaming
Services Agreements between AWS and other providers of wireless
telecommunications service, and AWS would like Company to receive such benefits
under the terms and conditions of this Agreement:

         WHEREAS, AWS provides Roamer Administration Services to owners and
operators of wireless telecommunications systems;

         WHEREAS, the Company owns and operates wireless telecommunications
system(s) identified on Exhibit A and would like to receive Roamer
Administration Services from AWS; and

         WHEREAS, AWS would like to provide the Company with Roamer
Administration Services subject to the terms and conditions of this Agreement;

         NOW, THEREFORE, in consideration of the mutual covenants and agreements
contained herein, and other good and valuable consideration, the parties hereby
agree as follows:

                                   Definitions

           As used herein, the following terms shall have the following
meanings:

         AS means the Administrative Services as more fully described in Exhibit
         --
B.

         CIBER means Cellular Intercarrier Billing Exchange Record as more fully
         -----
described in the CIBER Standard.

         CIBER Standard means the publication prepared by CIBERNET Corporation,
         --------------
a wholly-owned subsidiary of the Cellular Telecommunications Industry
Association, as a service to the wireless communications industry. Unless
specifically provided otherwise in this Agreement, all words and phrases defined
in the CIBER Standard shall have the meaning herein that they have therein.

         Claims means any claims, liabilities, damages, costs and expenses
         ------
(including reasonable attorneys' fees) asserted by a third party against a party
to this Agreement.
<PAGE>

         CMRS or Service means Commercial Mobile Radio Service.
         ---------------

         EDS PCC means EDS Personal Communications Corporation.
         -------

         EDS PCC Agreement means that certain Interoperator Agreement dated
         -----------------
January 3, 1997, between AWS and

         EDS PCC for certain services, as that Agreement may be amended,
         -------
extended or renegotiated from time to time.

         ESN means the Electronic Serial Number that is encoded in a wireless
         ---
telephone set by the manufacturer and which is broadcast by such telephone.

         Expenses means those costs and expenses related to providing the
         --------
Roaming Administration Services set forth in Exhibit C, as may be amended from
time to time by AWS.

         Fees means those fees for Roaming Administration Services set forth in
         ----
Exhibit C, as may be amended from time to time by AWS.

         Incollect Obligations means those obligations of the Company to AWS and
         ---------------------
Other Wireless Carriers that arise from Roaming by the Company's subscribers on
other wireless systems. These Incollect Obligations accrue separate for each of
AWS and each Other Wireless Carrier.

         Intercarrier Roaming Services Agreement means an agreement entered into
         ---------------------------------------
by two facilities-based providers of CMRS under which each carrier agrees to
provide Service to the subscribers of the other carrier and which sets forth
other terms and conditions of the provision of such Service, including but not
limited to price, payment or settlement, and fraud liability terms, as the
agreement may be amended, extended or renegotiated from time to time.

         ISS means Intercarrier Settlement Services as more fully described in
         ---
Exhibit B.

         MIN means the ten-digit Mobile Identification Number which is assigned
         ---
by a Home Carrier to each of its registered customers.

         NACN means the North American Cellular Network, Inc. and the SS7
         ----
signaling network owned and operated by the North American Cellular Network,
Inc.

         NPA/NXX combinations means the six-digit numerical combinations
         -------
assigned by regulatory authorities to identify the area code and telephone
number prefix for Service.

         NSS means Net Settlement Services as more fully described in Exhibit B.
         ---

                                       2
<PAGE>

         Other Wireless Carriers means facilities-based providers of CMRS with
         -----------------------
whom AWS has entered an Intercarrier Roaming Services Agreement and which are
listed on Exhibit A-1.

         Outcollect Obligations means obligations owed to the Company by AWS and
         ----------------------
Other Wireless Carriers arising from Roaming by the subscribers of these
companies on the Company System. These Outcollect Obligations accrue separately
for each of AWS and each Other Wireless Carrier.

         PRV means Positive Roamer Verification services as more fully described
         ---
in Exhibit B.

         Roamer means a customer of a wireless carrier who seeks Service within
         ------
a geographic area served by another wireless carrier.

         Roaming Administrative Services means the services described in Exhibit
         -------------------------------
B, including AS, FV, ISS, NSS, PRV and XLI, together with the services that may
be provided in connection with the access to the Intercarrier Roaming Services
Agreements entered into between AWS and Other Wireless Carriers.

         Serving Carrier means a Party who provides Service for registered
         ---------------
customers of another Party while such customers are in the geographic area where
the Serving Carrier, directly or through subsidiaries, provides Service.

         Settlement Period shall mean each one-month period of time commencing
         -----------------
at 12:01 a.m. Pacific Standard Time on the sixteenth day of a given calendar
month and ending at 12:00 midnight on the fifteenth day of the immediately
following calendar month.

         XLI means a certain type of PRV service as more fully described in
         ---
Exhibit B.

         Company System means the wireless telecommunications system(s) owned
         --------------
and operated by the Company as identified on Exhibit A.

                                       3
<PAGE>

                                   Agreement

     1.   Access to Intercarrier Roaming Services Agreements. During the term
          --------------------------------------------------
of this Agreement, AWS will make available to Company the benefits of the
Intercarrier Roaming Services Agreements between AWS and Other Wireless Carriers
listed on Exhibit A-1, subject to the consent of such Other Wireless Carriers
and subject to the Company being a member in good standing of the NACN. The
Company will permit the subscribers of such Other Wireless Carriers to use the
facilities of the Company under the terms and conditions of the applicable
Intercarrier Roaming Services Agreements. AWS may amend Exhibit A-1 by adding
Other Wireless Carriers who have agreed to extend an Intercarrier Roaming
Services Agreement to the Company or by deleting Other Wireless Carriers who
have either revoked the consent to extend an Intercarrier Roaming Services
Agreement to the Company or with whom the Intercarrier Roaming Services
Agreement has terminated or expired, any such amendment to be effective no
earlier than 7 days after the date such notice is given.

     1.1  AWS Authority and Separate Rate Agreements. The Company agrees that
          ------------------------------------------
AWS has full authority to negotiate terms, amendments of and addenda to the
Intercarrier Roaming Services Agreements, administer the Intercarrier Roaming
Services Agreements and settle disputes under the Intercarrier Roaming Services
Agreements on behalf of the Company and that the Company will be bound by and
comply with such terms, amendments, addenda, administrative decisions and
settlements. The Company may, at its option, choose to negotiate a separate rate
for roaming Service with any or all of the Other Wireless Carriers. In order to
have these separate rates included within the Roamer Administration Services,
the Company must provide AWS with written documentation verifying the rates at
least thirty (30) days prior to the effective date for such rates.

     1.2  Separate Liability. The Company is liable for all of its obligations
          ------------------
under each Intercarrier Roaming Services Agreement in which it participates,
including but not limited to payment obligations and fraud liability
obligations. AWS will make available a copy of applicable Intercarrier Roaming
Services Agreements within 30 days of request by the Company.

     1.3  Effect of Intercarrier Roaming Services Agreements. Each Intercarrier
          --------------------------------------------------
Roaming Services Agreement, as may be amended with respect to the Company under
section 1.1 above, supplies the terms and conditions of roaming services with
respect to each Other Wireless Carrier. AWS maintains full control to continue
or to terminate or let expire any Intercarrier Roaming Services Agreement.
Nothing in this Agreement obligates AWS to enter into or to continue any
Intercarrier Roaming Services Agreement with any Other Wireless Carrier. AWS
will notify the Company no less than thirty (30) days in advance of any
termination by AWS or expiration of any Intercarrier Roaming Services Agreement.

     1.4  Fraud Control. The Company shall take reasonable actions to control
          -------------
fraudulent Roamer usage when acting as a Serving Carrier to be consistent with
the Intercarrier Roaming Services Agreements, including without limitation using
SS-7 connections through the NACN which perform validation functions. The
Company shall use commercially reasonable efforts to provide each Other Wireless
Carrier with real-time visibility of call detail records delivered

                                       4
<PAGE>

through a network compatible with AT&T's network. Such information shall be
delivered within one hour of the applicable call. In the event that the Company
provides such a real-time visibility system, the Company shall not be liable in
any event for a temporary failure of the system unless the Company has been
notified of such failure by the Other Wireless Carrier and the Company does not
take commercially reasonable steps to remedy the failure. If the Company has
been so notified and has so failed to take such commercially reasonable steps,
the Company shall be liable for all unauthorized usage attributed to the Other
Wireless Carrier's subscribers during the period from the time the Company was
notified of the problem to the time that the problem has been resolved to the
reasonable satisfaction of the Other Wireless Carrier.

     1.5  Allocation of Roamer Revenues and Roamer Expenses. AWS will treat the
          -------------------------------------------------
Company as an affiliate of AWS for administrative purposes in collecting and
paying amounts owed to the Company and owed by the Company under the applicable
Intercarrier Roaming Services Agreement. The Company acknowledges and agrees
that amounts owed to the Company from Other Wireless Carriers will be collected
by AWS, intermingled with other funds owed to AWS and then distributed to the
Company based upon the amounts owed to the Company for Roamer usage by
subscribers of the Other Wireless Carriers. The Company further acknowledges and
agrees that AWS will make payments for the Company to Other Wireless Carriers
based on the reports of Roamer usage by subscribers of the Compay on the systems
of the Other Wireless Carriers. AWS will recover these amounts through the NSS
functions described in Exhibit B.

     2.   Roaming Administration Services. During the term of this Agreement,
          -------------------------------
AWS hereby agrees to make available Roaming Administration Services to the
Company, subject to the terms of this Agreement. The Roaming Administration
Services are set forth in Exhibit B, which may be amended by AWS from time to
time upon written notice to the Company.

     2.1  Effect of EDS PCC Agreement. The Company acknowledges that AWS
          ---------------------------
receives certain of the Roaming Administration Services under the EDS PCC
Agreement. In the event the EDS PCC Agreement terminates or expires, AWS'
obligations to provide such Roaming Administration Services will cease. AWS will
give the Company notice promptly following its receipt of notice of termination
from EDS PCC and will give prior notice of any cessation of Roaming
Administration Services under this section 2.1. AWS will offer to resume such
services (on such terms as it determines at the time of such offer) in the event
that it extends or continues with EDS PCC, or enters into a new agreement with
any other provider, with respect to such services. Nothing in this Agreement
obligates AWS to extend, continue or enter into a new EDS PCC Agreement. The
Company agrees to comply with reasonable requests made by AWS in order to comply
with and administer the EDS PCC Agreement.

     2.2  Rates for Service. The Company shall pay AWS Fees and Expenses for the
          -----------------
Roamer Administration Services as set forth on Exhibit C attached hereto. AWS
may modify the Fees and Expenses set forth in Exhibit C upon thirty (30) days
prior written notice to the Company. Amounts owed each month for Fees and
Expenses will be included as amounts owed to AWS in the NSS function described
in Exhibit B.

                                       5
<PAGE>

     3.   Taxes. Unless the Company provides a certificate of exemption or other
          -----
evidence acceptable to appropriate taxing authorities, the Company shall pay any
applicable federal, state or local sales, use, public utility, gross receipts or
other taxes, fees or charges imposed on AWS as a result of (a) the roaming
services received by the Company under the Intercarrier Roaming Services
Agreements and (b) providing the Roaming Administration Services to the Company.
Such taxes will be included in bills when imposed or required by law and shall
be paid by the Company in accordance with this Agreement.

     4.   Payment of Net Amounts.
          ----------------------

     4.1  Amounts Owed to AWS. The Company will pay AWS in full any amounts owed
          -------------------
to AWS after the NSS procedure described in Exhibit B has occurred, including
amounts owed to AWS or Other Wireless Carriers, on or before the fifteenth day
of the month immediately following the close of a Settlement Period, provided
the Company has received the bill for such amounts at least five (5) business
days prior to such payment date. If the Company receives the bill later than
such time, the Company shall pay the bill within ten (10) days of its receipt by
the Company. Payments will be submitted to: AT&T Wireless Services, Inc., 7277
164/th/ Avenue, N.E., Redmond, Washington 98052 ATTN: Billing and Intercarrier
Settlement Services.

     4.2  Amounts Owed to the Company. AWS will pay the Company in full any
          ---------------------------
undisputed amounts owed to TeleCorp after the NSS procedure described in Exhibit
B has occurred by AWS or Other Wireless Carriers, (a) for amounts owed by AWS,
on or before the fifteenth day of the month immediately following the close of a
Settlement Period, (b) for amounts owed by Other Wireless Carriers, together
with the net settlement for the month following the date AWS receives payment
from the Other Wireless Carriers. Payments will be submitted to: Holding
Company, 1010 N. Glebe Road, Arlington, VA 22201, ATTN: Controller.

     4.3  Time. The Company acknowledges and understands that, AWS will pay
          ----
Other Wireless Carriers for the Company subscribers' roaming usage prior to
receiving payment from the Company. Accordingly, the Company acknowledges and
agrees that time is of the essence and will make timely payments to AWS of all
amounts set forth in each bill after the NSS procedures described in Exhibit B
have occurred. The Company is strictly liable to make timely payments hereunder,
and such liability is not relieved by any dispute that the Company may have with
AWS, Other Wireless Carriers or any other third party.

     4.4  Late Payment. If either party fails to make any payment to the other
          ------------
party when due hereunder, interest shall be paid, from the date due until paid
in full, at a rate of 1.5% per month or portion thereof. In no event shall
interest hereunder accrue at a rate that is in excess of the maximum rate
permitted by applicable law.

     5.   Compatibility with AWS Systems. AWS will establish and, from time to
          ------------------------------
time, enhance the systems that provide information used in performing functions
related to either the EDS PCC Agreement or Intercarrier Roaming Services
Agreements, including, but not limited

                                       6
<PAGE>

to, enhancements to billing systems. The Company will maintain compatibility
with these systems and system enhancements, including but not limited to the
CIBER format for billing records. The Company will be responsible for the costs
and expenses it incurs in maintaining this compatibility.

     6.   Indemnification. The Company will defend, indemnify and hold AWS,
          ---------------
its parent, subsidiaries and affiliates, and the officers, directors, employees
and representatives of each of them harmless from and against any Claims arising
from or made in connection with (a) any access or use (or inability to access or
use) of roaming Service by the Company or any subscriber of the Company, on the
system of AWS or any Other Wireless Carrier, (b) any access or use (or inability
to access or use) of roaming Service on the Company's wireless system by AWS or
an Other Wireless Carrier or a subscriber of AWS or an Other Wireless Carrier,
(c) any information provided by the Company to AWS, including without limitation
any rate information and suspected fraud information, (d) any unlawful,
negligent or otherwise wrongful act or failure to act of the Company or its
representatives, (e) a breach by the Company of any provision of this Agreement,
or (f) a breach by the Company of any obligation to or agreement with its
subscribers.

     7.   Limitation of Liability.
          -----------------------

     7.1  AWS SHALL NOT BE RESPONSIBLE TO THE COMPANY FOR ANY INDIRECT,
INCIDENTAL, CONSEQUENTIAL OR SPECIAL DAMAGES ARISING OUT OF OR IN CONNECTION
WITH AWS' PERFORMANCE UNDER THIS AGREEMENT, INCLUDING WITHOUT LIMITATION, ANY
DAMAGE TO OR LOSS OF REVENUES, BUSINESS OR GOODWILL. FURTHER, THE COMPANY
ACKNOWLEDGES THAT IN PERFORMING ITS OBLIGATIONS HEREUNDER AWS WILL RELY UPON
INFORMATION AND REPORTS PROVIDED TO AWS BY THIRD PARTIES. THE COMPANY AGREES
THAT AWS MAY RELY UPON SUCH INFORMATION IN PERFORMING ITS OBLIGATIONS HEREUNDER,
AND AWS SHALL NOT BE RESPONSIBLE OR LIABLE FOR THE ACCURACY OF ANY INFORMATION
IT RECEIVES FROM THIRD PARTIES IN PERFORMING ITS OBLIGATIONS UNDER THIS
AGREEMENT. IN NO EVENT WILL AWS' LIABILITY TO THE COMPANY, IN THE AGGREGATE,
EXCEED THE AMOUNT PAID IN FEES BY TELECORP UNDER THIS AGREEMENT DURING THE FIRST
TWELVE-MONTH PERIOD OF THE TERM OF THIS AGREEMENT. THIS SECTION 7.1 WILL SURVIVE
THE TERMINATION OR EXPIRATION OF THIS AGREEMENT.

     7.2  Neither of the parties will be liable for nonperformance or defective
or late performance of any of its obligations under this Agreement to the extent
and for such periods of time as such nonperformance, defective performance is
due to reasons outside such party's control, including, without limitation, acts
of God, war, acts (including failure to act) of any governmental authority,
riots, revolutions, fire, floods, explosions, sabotage, nuclear incidents,
lightning, weather, earthquakes, storms, sinkholes, epidemics, strikes or delays
of suppliers, subcontractors, Other Wireless Carriers or EDS PCC. Neither party
shall be required to settle any

                                       7
<PAGE>

labor dispute in any manner which is deemed by that party to be less than
totally advantageous, in that party's sole discretion.

     8.   Confidentiality.
          ---------------

     8.1  Each of the parties hereto hereby covenants and agrees that, during
the term of this Agreement and thereafter, neither it, nor any of its employees,
agents, officers or directors, will at any time make use of, divulge or disclose
to any person, firm or corporation any trade secrets or confidential or
proprietary information about the other party, its business, financial
condition, operations or otherwise (including, without limitation, any
information concerning the other party's subscribers, their names, addresses, or
telephone numbers, the terms and conditions of each Intercarrier Roaming
Services Agreement and its amendments and addenda), whatever the source of such
confidential or proprietary information. Specifically, and without limitation,
the Company acknowledges that all operational user's guides, manuals, computer
application programs, written procedures or other systems documentation
furnished to it by AWS is the sole property and proprietary information of AWS.
This confidentiality agreement shall not apply to information which is in the
public domain through no act of the party desiring to disclose. Information
contained in documents shall be considered confidential or proprietary if it
relates to information described above or the content and context of the
information is indicative of a desire to maintain confidentiality, whether or
not the document is specifically marked "confidential" or "proprietary".

     8.2  Each party agrees that such confidential or proprietary information
concerning the other party shall only be divulged or disclosed to its employees
who have a valid business reason to know such information and then only to the
extent required for the performance of such employee's duties.

     8.3  Nothing herein shall restrict the right of any party to disclose
confidential or proprietary information which is ordered to be disclosed
pursuant to judicial or other lawful governmental action, but only to the extent
so ordered, or as otherwise required by applicable law or regulation. If either
party is served with process to obtain any confidential or proprietary
information or subscriber records of the other party, that party shall
immediately notify the other party and permit the other party to conduct the
defense against disclosure.

     8.4  Upon termination of this Agreement, each party shall, upon written
request of the other party, return to the other all confidential and proprietary
information concerning the other which exists in written or electronic form.

     8.5  Each of the parties acknowledges and confirms that any failure on its
part to adhere strictly to the terms and conditions of this paragraph is likely
to cause substantial and irreparable injury to the other party. Accordingly,
each party confirms and agrees that, in addition to all other remedies to which
the other party may be entitled under this Agreement or at law or in equity, the
other party shall be entitled to specific performance and other equitable
relief, including temporary relief.

                                       8
<PAGE>

     9.   Term and Termination.
          ---------------------

     9.1  This Agreement shall run for an initial term of two years, commencing
on the date of this Agreement. It shall automatically renew for additional
successive terms of one year each, unless either party gives the other party
written notice of its intent not to renew at least ninety (90) days prior to the
termination of the then-current term.

     9.2  Either party may terminate this Agreement (except for any obligations
which survive termination) for any reason or for no reason upon one hundred
eighty (180) days prior written notice to the other party.

     9.3  Either party may terminate this Agreement (except for any obligations
which survive termination) for any of the following reasons:

          9.3.1  Upon material breach of the other party which is not cured or
     for which cure is not reasonably commenced within 30 days after notice of
     claimed breach;

          9.3.2  Immediately by either party, after reasonable prior notice, if
     the other party's operations materially and unreasonably interfere with its
     operations and such interference is not eliminated within 10 days;

     9.4  AWS may terminate this Agreement (except for any obligations which
survive termination) in the event that the Company is no longer a member in good
standing with the NACN.

     9.5  AWS may terminate this Agreement with respect to any Intercarrier
Roaming Services Agreement in accordance with Section 1.

     9.6  AWS may terminate its obligations with respect to certain provisions
under this Agreement:

          9.6.1  with respect to the EDS PCC Agreement in the event such
     agreement expires or terminates; and

          9.6.2  with respect to the Roaming Administration Services as set
forth in Section 2.1 above.

     9.7  Section 1 shall survive any termination by AWS pursuant to Section 9.4
or 9.5.


     10.  Events Upon Termination. Upon termination of this Agreement for
          -----------------------
whatever reason, each party shall immediately (or upon final accounting) pay all
amounts owing to the other parties hereunder, whether due or to become due.

                                       9
<PAGE>

     11.   Representations and Warranties of the Company. The Company hereby
           ---------------------------------------------
represents and warrants to AWS the following:

     11.1  It is duly organized and validly existing under the laws of the
     jurisdiction of its organization.

     11.2  It has full power and authority to execute and perform this
Agreement.

     11.3  The execution, delivery and performance of this Agreement has been
duly authorized by all necessary action on its part and is binding and
enforceable against it.

     11.4  It is and for the term of this Agreement will remain qualified to
hold a wireless operating license for the areas listed on Schedule A pursuant to
the rules and regulations of the Federal Communications Commission any state
authority with jurisdiction over the areas identified on Schedule A.

     12.   Notices and Other Communications.
           --------------------------------

     12.1  All notices required hereunder shall be in writing and shall be
deemed to have been duly delivered effective upon receipt if personally
delivered, or upon mailing if mailed by prepaid overnight express service,
addressed to the following:

                   If to AWS:

                   AT&T Wireless Services, Inc.
                   Carrier Relations
                   7277 164/th/ Avenue, N.E.,
                   Redmond, Washington 98052


                   With a copy to:

                   AT&T Wireless Services, Inc.
                   7277 164/th/ Avenue, N.E.,
                   Redmond, Washington 98052
                   Attn:  Legal Department.

                   If to the Company:

                   Holding Company
                   1010 N. Glebe Road
                   Arlington, VA 22201
                   Attn:  Product Development-Roaming

                                      10
<PAGE>


              With a copy to:
              Holding Company
              1010 N. Glebe Road
              Arlington, VA 22201
              Attn:  Legal Department

     12.2  For purposes of communication in order to administer this Agreement
effectively, the parties designate the following contact persons for the subject
matters set forth for them below. Either party may change the information with
respect to its designated contacts under this Section 12.2 upon oral or written
notice to the other party.

              TeleCorp Customer Care Contact
              Name: Scott Weismiller Tel: Tel: 703-236-1100 Fax: 703-236-1101

              TeleCorp Switch Update/Technical Contact
              Name: Curt Gervelis Tel: 703-236-1100 Fax: 703-236-1101

              TeleCorp Finance/Accounting Contact
              Name: Chris Schrand/Bill Baker Tel: 703-236-1100 Fax: 703-236-1101

              [AWS Customer Care Contact
              Name: David Mansisidor Tel: 425-803-8821 Fax: 425-828-1390]

              [AWS Switch Update/Technical Contact
              Name: David Mansisidor Tel: 425-803-8821 Fax: 425-828-1390]

              [AWS Finance/Accounting Contact
              Name: Mary Hawes Tel: 425-828-1308 Fax: 425-828-1390]

     13.   Miscellaneous Provisions.
           ------------------------

     13.1  Attorneys' Fees and Costs. In the event of any action at law or in
           -------------------------
equity concerning the enforcement or interpretation of the terms of this
Agreement, the prevailing party shall be entitled to reimbursement for
reasonable attorneys' fees, costs, and necessary disbursements in addition to
any other relief to which it may show itself to be entitled.

     13.2  No Joint Venture. Nothing in this Agreement is intended, or shall be
           ----------------
construed, to create a joint venture, partnership or other common business
entity as among AWS and TeleCorp. Neither of the parties shall have the
authority to accept legal process on behalf of the other party. Nothing herein
gives TeleCorp or AWS claim to the subscribers of the other or to revenues of
the other derived from its respective system. Both parties shall be solely
responsible for the operation of its systems or businesses, including but not
limited to payment of wages, benefits, taxes for employees and sales or income
taxes.

                                      11
<PAGE>

         13.3  Governmental Approval. The performance of any obligations of any
               ---------------------
party hereunder, or the exercise of any rights hereunder by any party hereto
that may require FCC or other governmental authority approval, shall be subject
to obtaining such approval. Both parties agree to take no action under this
Agreement which may place the other party in non-compliance with known and
applicable government regulations.

         13.4  Governing Law. This Agreement shall be construed under and in
               --------------
accordance with the Laws of the State of Washington.

         13.5  Assignment. This Agreement and the duties and obligations
               ----------
hereunder may not be assigned by either party without the express written
consent of the other party and an agreement by the assignee to be fully bound by
the terms and conditions hereof; provided, however, that such consent will not
be unreasonably withheld; and, provided further, that AWS may assign its rights
and obligations to an affiliate without obtaining the consent of the Company.
The Company acknowledges that AWS may subcontract any or all of its duties under
this Agreement to a third party. In the event AWS assigns this Agreement to a
third party, the Company may terminate this Agreement upon 90 days' written
notice within 30 days of such assignment.

         13.6  No Third-Party Beneficiary. This Agreement is not intended, nor
               --------------------------
shall it be construed, to create or convert any right in or upon any person or
entity not a party to this Agreement, unless specifically set forth in this
Agreement.

         13.7  Parties Bound. This Agreement shall be binding upon and inure to
               -------------
the benefit of the parties hereto and their respective heirs, executors,
administrators, legal representatives, successors and assigns where permitted by
this Agreement.

         13.8  Severability. In case any one or more of the provisions contained
               ------------
in this Agreement shall for any reason be held by any arbitration tribunal or
court of competent jurisdiction to be invalid, illegal or unenforceable in any
respect, such invalidity, illegality or unenforceability shall not affect any
other provision thereof, and this Agreement shall be construed as if such
invalid, illegal, or unenforceable provisions were deleted, and replaced with
enforceable provisions, which as nearly as possible, give effect to the intent
of such invalid, illegal or unenforceable provisions.

         13.9  Entire Agreement. This Agreement constitutes the sole and only
               ----------------
agreement of the parties with respect to the services described herein and
supersedes any prior understanding or written or oral agreements between the
parties respecting the within subject matter. In the event another form or
invoice is used for provision of the services and such form or invoice contains
terms or conditions different from those set forth herein, the parties agree
that the language of this Agreement shall control.

         13.10 Section Headings. The headings of the several sections and
               ----------------
paragraphs of this Agreement are inserted for convenience of reference only and
are not intended to be part of or to affect the meaning or interpretation of
this Agreement.

                                       12
<PAGE>

         13.11 No Waiver. Either party's failure at any time to enforce any of
               ---------
the provisions of this Agreement or any right with respect thereto, or to
exercise any option herein provided, will in no way be construed to be a waiver
of such provisions, rights or options or in any way to affect the validity of
this Agreement. The exercise by either party of any rights or options herein
shall not preclude or prejudice the exercising thereafter of the same or other
rights under this Agreement.

         13.12 Dispute Resolution.
               ------------------

         (a)   All claims and disputes relating in any way to the performance,
interpretation, validity, or breach of this Agreement, including but not limited
to a claim based on or arising from an alleged tort, shall be resolved as
provided in this Section 13.12. It is the intent of the parties that any
disagreements be resolved amicably to the greatest extent possible.

         (b)   If a disagreement cannot be resolved by the representatives of
the parties with day-to-day responsibility for this Agreement, such matter shall
be referred to an executive officer of each of the parties. The executive
officers shall conduct face-to-face negotiations at a neutral location or such
other location as shall be mutually agreed upon. If these representatives are
unable to resolve the dispute within ten business days after either party
requests the involvement of the executive officers, then either party may, but
is not required to, refer the matter to mediation or arbitration, as applicable
in accordance with this Section 13.12.

         (d)   In any case where the amount claimed or at issue is Five Hundred
Thousand Dollars ($500,000.00) or more and the parties are unsuccessful in
resolving the disagreement, the parties agree to submit the disagreement to
non-binding mediation upon written notification by either party. The parties
shall mutually select an independent mediator experienced in telecommunications
system disputes. The specific format for the mediation shall be left to the
discretion of the mediator. If mediation does not result in resolution of the
disagreement within thirty days of the initial request for mediation, then
either party may, but is not required to, refer the matter to arbitration.

         (e)   Any disagreement not finally resolved in accordance with the
foregoing provisions of this Section 13.12 shall, upon written notice by either
party to the other, be resolved by final and binding arbitration. Subject to
this Section, such arbitration shall be conducted through, and in accordance
with the rules of, JAMS/Endispute. A single neutral arbitrator shall decide all
disputes. Each party shall bear its own expenses with respect to the
arbitration, except that the costs of arbitration proceeding itself, including
the fees and expenses of the arbitrator, shall be shared equally by the parties.
The arbitration shall take place in a neutral location selected by the
arbitrator. The arbitrator may permit discovery to the full extent permitted by
the Federal Rules of Civil Procedure or to such lesser extent as the arbitrator
determines is reasonable. The arbitrator shall be bound by and strictly enforce
the terms of this Agreement. The arbitrator shall make a good faith effort to
apply applicable law, but an arbitration decision and award shall not be subject
to review because of errors of law. The arbitrator shall have the sole authority
to resolve issues of the arbitrability of any disagreement, including the
applicability or running of any applicable statute of limitation. The arbitrator
shall

                                       13
<PAGE>

not have power to award damages in connection with any dispute in excess of
actual compensatory damages nor to award punitive damages nor any damages that
are excluded under this Agreement and each party irrevocably waives any claim
thereto. The award of any arbitration shall be final, conclusive and binding on
the Parties. Judgment on the award may be entered in any court having
jurisdiction over the Party against which the award was made. Nothing contained
in this Section 13.12 shall be deemed to prevent either party from seeking any
interim equitable relief, such as a preliminary injunction or temporary
restraining order, pending the results of the arbitration. The United States
Arbitration Act and federal arbitration law shall govern the interpretation,
enforcement, and proceedings pursuant to the arbitration clause in this
Agreement.

         (f)   No action or arbitration, regardless of form, may be brought by
either party more than two (2) years from the date of the event which gave rise
to such action.

                                       14
<PAGE>

         IN WITNESS WHEREOF, the parties have executed this Agreement as of the
date and year first above written.


                                     AT&T Wireless Services, Inc.

                                     By: __________________________________
                                     Name:
                                     Title:

                                     HOLDING COMPANY

                                     By: __________________________________
                                     Name:
                                     Title:

                                       15
<PAGE>

                                   EXHIBIT A

                            Holding Company System

     [To be updated and provided at Closing]

                                       16
<PAGE>

                                  EXHIBIT A-1

                            Other Wireless Carriers

                    [To be updated and provided at Closing]

                                       17
<PAGE>

Effective 7/16/98

                                  Exhibit A-1

             Carrier_Name                                  Carrier_Shortname
VALLEY TELECOMMUNICATIONS COMPANY                      VALLEY TELECOMMUNICATIONS
WESTERN WIRELESS CORPORATION                           WESTERN WIRELESS
COMCAST CELLULAR CORPORATION                           COMCAST CELLULAR
HOUSTON CELLULAR TELEPHONE CO                          HOUSTON CELL
WESTEL - INDIANAPOLIS TELEPHONE COMPANY                WESTEL
AT&T WIRELESS SERVICES, INC.                           AWS
SYGNET COMMUNICATIONS INC.                             SYGNET COMM INC.
UNITED STATES CELLULAR CORP                            U.S. CELLULAR
MERCURY CELLULAR INCORPORATED                          MERCURY CELLULAR
ALLTEL MOBILE COMMUNICATIONS                           ALLTEL
PALMER WIRELESS INC.                                   PALMER WIRELESS
GALVESTON CELLULAR TELEPHONE CO.                       GALVESTON CELL
PETROLEUM COMMUNICATIONS                               PETROCOM
SANTA CRUZ CELLULAR TELEPHONE CO.                      SANTA CRUZ CELL.
APPALACHIAN CELLULAR                                   APPALACHIAN CELLULAR
SPRINGWICH CELLULAR LTD PARTNERSHIP                    SNET CELLULAR
ARCTIC SLOPE TELECOMM. & CELLULAR, INC.                ARCTIC SLOPE CELLULAR
DOBSON CELLULAR SYSTEMS OF KS/MO                       DCS OF KS/MO
BACHOW/COASTEL OPERATIONS, INC.                        COASTEL COMMUNICATIONS
ALLEGAN CELLULAR L.P.                                  ALLEGAN CELLULAR
EASTERBROOKE CELLULAR CORP - RCM                       EASTERBROOKE CELLULAR
LAKE HURON CELLULAR CORPORATION                        LAKE HURON CELLULAR
TEXAS 16 CELLULAR TELEPHONE COMPANY                    TEXAS 16 CELLULAR
TRIAD CELLULAR PREVIOUSLY C-1 N. TEXAS                 TRIAD CELLULAR
METACOMM CELLULAR PARTNERS                             METACOMM CELLULAR
BLACKWATER CELL/DOUGLAS TELECOMMUNICATIONS             BLACKWATER CELLULAR
ALPHA CELLULAR                                         C-1 COLUMBUS
CELLULAR COMM OF PUERTO RICO INC                       CCPR
PRICELLULAR CORPORATION                                PRICELLULAR
GREAT LAKES OF IOWA, INC.                              C-1 GREAT LAKES OF IOWA
DOBSON CELLULAR SYSTEMS INCORPORATED                   DOBSON CELLULAR
CAL-ONE CELLULAR                                       CAL-ONE CELLULAR
MERCURY COMMUNICATIONS                                 MERCURY COMMUNICATIONS
HLD CELLULAR                                           HLD CELLULAR
IFC CELLULAR PARTNERS                                  C-1 FREDERICK
BLUE MOUNTAIN CELLULAR                                 BLUE MOUNTAIN CELLULAR
CELLULAR ONE OF SOUTHWEST FLORIDA                      C-1 SW FLORIDA
UNIVERSAL TELECELL, INC.                               UNITEL INC.

                                       18
<PAGE>

                                   EXHIBIT B

                        Roaming Administration Services

1.   Administration Services (AS)

The AS will include various services that AWS will perform to manage the
Company's roaming program.

1.1  Reports and Bills. Each month during the term of this Agreement, within a
     -----------------
reasonable period of time after receipt by AWS of information regarding the
Roamer activity during the prior Settlement Period, AWS shall provide the
Company with a report summarizing Roamer activity during the prior Settlement
Period.

1.2  Exchange of Information. AWS shall provide Other Wireless Carriers and the
     -----------------------
North American Cellular Network with information (including, without limitation,
NPA/NXX and number range combinations) provided to AWS by the Company pursuant
to the Intercarrier Roamer Services Agreement between AWS and the Company that
will enable the Company's subscribers to roam in the markets owned by Other
Wireless Carriers. Further, AWS shall provide the Company with information
(including, without limitation, NPA/NXX combinations and MINs) provide to AWS by
Other Wireless Carriers and the NACN pursuant to roaming agreements that will
enable the subscribers of Other Wireless Carriers to roam in the wireless
systems identified in Exhibit A-1.

1.3  Outcollect Table Maintenance. In the event that the Company uses CBIS as
     ----------------------------
its billing vendor, AWS will maintain the Macro/Cell tables necessary to bill
subscribers of AWS and Other Wireless Carriers for use of the  Company
network. Specifically, AWS agrees to maintain the Roamer Outcollect Maintenance
(070101) and roamer Surcharge Maintenance (070102) tables including bi-weekly
updates of new NPA/NXX information, maintenance required by changes to rate
agreements and corrections identified through the course of AWS' regular
operations work.

1.4  Fraud Brownout Notifications. AWS agrees to serve as the request processor
     ----------------------------
and single point of contact between the Company, on the one hand, and AWS and
Other Wireless Carriers, on the other hand, for the exchange of suspected
fraudulent use notifications and NPA/NXX pull and reload requests related to
fraudulent use of Company NPA/NXX's on the networks of AWS and Other Wireless
Carriers and the NPA/NXX's of AWS and Other Wireless Carriers on the network of
the Company. AWS will receive and forward all requests on a daily (Monday -
Friday) basis to the appropriate party for action. In addition, AWS agrees to
maintain and distribute as requested historical data regarding fraud pull and
reload request data.

                                       19
<PAGE>

1.5    Rate Monitoring. AWS will monitor incollect rates charged to the Company
       ---------------
and outcollect rates charged by the Company. If an incorrect roaming rate is
charged by the Company to an Other Wireless Carrier, and the Other Wireless
Carrier invoices AWS for amounts charged in excess of the amounts that should
have been charged under the applicable Intercarrier Roaming Services Agreement,
AWS shall refund all amounts in excess of the contract rate back to the Other
Wireless Carrier within forty-five days of notification by the Other Wireless
Carrier. If an incorrect roaming rate is charged to the Company by an Other
Wireless Carrier so that the amounts charged in a month are more than $200 over
the amounts that should have been charged under the applicable Intercarrier
Roaming Services Agreement, AWS will invoice the Other Wireless Carrier for all
amounts in excess of the contract rate. AWS shall not be responsible for any
amounts undercharged by AWS on behalf of the Company to any Other Wireless
Carrier.

2.     Full Visibility (FV) Services - Optional Service. FV services are adjunct
       ------------------------------------------------
to XLI service. FV provides a mechanism for receiving transaction information on
all call attempts made by a Roamer who subscribes to a carrier using XLI while
roaming on a market serviced by the GTE TSI network for validation. The FV
services include the following features:

2.1    When a subscriber from a carrier using XLI is roaming in an area served
by GTE for validation is found negative in GTE's negative file, GTE sends a
visibility notification message which can then be used to report the activity.
When a subscriber from a carrier using XLI is roaming in an area served by GTE
for validation, and is not found in the GTE negative file, but has a valid
status in their industry file, GTE will send a visibility notification message
which can then be used to report the activity.

2.2    Additional options for updating visibility settings by NPA/NXX ranges or
by System Identification ("SID") or Billing Identification ("BID") are
available.

2.3    Home carrier enabling/disabling option by NPA/NXX range or by SID/BID
within a 45-day period.

2.4    Availability of cloning activity reports for Roamers on systems using GTE
and XLI.

3.     Intercarrier Settlement Services (ISS). With ISS, AWS will instruct EDS
       --------------------------------------
PCC to edit roaming records to verify the billable status of these records.
These edits will be performed in accordance with the then current CIBER
standards. AWS will also provide certain standard reports in connection with
these edits.

3.1    Edits. The records will be edited against the CIBERNET standards, using a
       -----
60-day standard for the Call Age Edit. Any records which do not satisfy these
standards will be returned to the serving carrier.

3.1.1  Negative File Edit

                                       20
<PAGE>

3.1.2    CIBER Edit
3.1.3    NPA/NXX Edit - Proper Routing of Call
3.1.4    Call Age Edit
3.1.5    Out-of-Sequence Batch Edits
3.1.6    Duplicate Call Edit
3.1.7    Roamer Agreement Edit
3.1.8    Out of Balance Edit
3.1.9    Invalid Record Type Edit
3.1.10   Incorrect Rate Edit
3.1.11   Additional Edits Per CIBER Standard Table 3


3.2    Reports. The following reports reflect activity within a settlement
       -------
cycle. Each report is produced at the end of each settlement cycle (the 1st
through the 15th of the calendar month and the 16th of a calendar month through
month end).

3.2.1  Incollect Reports which summarize the amounts owed by the Company for
Roamer calls to each of AWS and each Other Wireless Carrier.

3.2.2  Outcollect Reports which summarize the amounts owed to the Company for
Roamer calls from each of AWS and each Other Wireless Carrier.

3.2.3  Net Settlement Reports which summarize the net amount owed to or owed by
the Company for Roamer calls with respect to each of AWS and each Other Wireless
Carrier.

4.     Net Settlement Services (NSS)
       -----------------------------

4.1    Clearinghouse Functions. AWS shall provide Roamer clearinghouse functions
       -----------------------
for the Company, such that the Company's Incollect Obligations are netted
against the Company's Outcollect Obligations for AWS and each Other Wireless
Carrier. To the extent that the Incollect Obligations, Fees and Expenses exceed
the net Outcollect Obligations with respect to AWS or with respect to any Other
Wireless Carrier, the Company shall pay such net Incollect Obligations, Fees and
Expenses to AWS. To the extent that net Outcollect Obligations exceed net
Incollect Obligations, Fees and Expenses with respect to AWS or any Other
Wireless Carrier, AWS shall pay such net Outcollect Obligations to TeleCorp.

4.2    Fraud Settlement Functions. AWS will invoice Other Wireless Carriers for
       --------------------------
Roamer fraud, under the terms of any Intercarrier Roaming Services Agreements in
place with Other Wireless Carriers. AWS will provide invoices to the Company for
Roamer fraud incurred by Other Wireless Carriers and make payments to Other
Wireless Carriers for these invoices. Information to be included in any invoice
to AWS or any Other Wireless Carrier must be in the format required by AWS, as
that format may change from time to time. This information must be

                                       21
<PAGE>

submitted to AWS sufficiently close to the date of the call record at issue in
order to permit AWS to invoice Other Wireless Carriers.

5.   Positive Roamer Verification (PRV) - Optional Service The PRV service will
     -----------------------------------------------------
provide TeleCorp with the ability to verify the billing status of Roamers from
Other Wireless Carriers not connected to TeleCorp through the NACN or other
network or carriers which provide alternative SS7 verification services. This
verification will be accomplished through comparison of the Roamer's MIN an ESN
combination with a database designed to identify potential fraudulent use. This
information can be used by the Company to deny service to callers when roaming
in the Company System.

                                       22
<PAGE>

                                   EXHIBIT C

                               Fees and Expenses

Service                   Fee
                          ---

PRV (optional)            $0.21 per unique ESN validation per each calendar day.

XLI (optional)            $0.16 per unique ESN validation per each calendar day.
                          $1000.00 per SID/BID minimum (waived if transaction
                          charges are greater than or equal to $1000.00)

FULL VISIBILITY           $0.025/transaction
(optional)                $500.00 for first SID/BID using FV.
                          $50.00 for additional SID/BIDs using FV.
                          $500.00 Installation - one time charge.

ISS                       $0.015 per outcollect record
                          $0.015 per incollect record

                          Monthly minimum:
                          Up to 100K records monthly: $2,000 per SID/BID flat
                          fee and no record fee.
                          Greater than 100K records monthly: $1,000 per SID/BID
                          plus record fee for records above 100K

CLEARINGHOUSE             $1000.00 per SID/BID
SET UP FEE

ROAM AGREEMENT            $25,000.00
SET UP FEE

CIBERNET Fees             $0.005 per outcollect amount dollar owed to the
                          Company.

Special Processing and    As agreed by the parties in writing
Reports

Clearinghouse Financial   $50.00 per market per Settlement Period
Reports

The Company will also pay all postage, handling, overnight mail fees, and any
other fees incurred by AWS as the result of complying with special requests from
the Company for services and reports not described in this Agreement or for
special modifications to any service or report.

AWS may modify the fees outlined above with 30 days' prior written notice.

                                       23