<PAGE>

                                                                  Exhibit 10.8.1

                   ROAMING ADMINISTRATION SERVICE AGREEMENT


     ROAMING ADMINISTRATION SERVICE AGREEMENT ("Agreement") made this 7th day of
January, 1999, 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 Tritel Inc. ("Tritel"), a Delaware corporation, with its
principal place of business at 1080 River Oaks Drive, Suite B-100, Jackson,
Mississippi 39208.


                                   Recitals
                                   --------

     WHEREAS, Tritel would like to receive certain benefits under Intercarrier
Roaming Services Agreements between AWS and other providers of wireless
telecommunications service, and AWS would like Tritel 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, Tritel 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 Tritel 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.
<PAGE>

     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.

     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 Tritel to AWS and Other
Wireless Carriers that arise from Roaming by Tritel'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 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.

                                      -2-
<PAGE>

     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.

     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 Tritel by AWS and Other
Wireless Carriers arising from Roaming by the subscribers of these companies on
the TRITEL 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.

     TRITEL System means the wireless telecommunications system(s) owned and
operated by Tritel 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 Tritel 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 Tritel being a member in good standing of the NACN. Tritel will
permit the subscribers of such Other Wireless Carriers to use the facilities of
Tritel 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 Tritel
or by deleting Other Wireless Carriers who have either revoked the consent to
extend an Intercarrier Roaming Services Agreement to Tritel or with whom the
Intercarrier Roaming Services Agreement has terminated or expired.

          1.1  AWS Authority. Tritel 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 Tritel
and that Tritel will be bound by and comply with such terms, amendments,
addenda, administrative decisions and settlements.

          1.2  Separate Liability.  Tritel is liable for all of its obligations
               ------------------
under each Intercarrier Roaming Services Agreement in which it participates,
including but not limited to payment obligations, preferred roaming status and
fraud liability obligations. AWS will make available a copy of applicable
Intercarrier Roaming Services Agreements upon request by Tritel.

          1.3  Effect of Intercarrier Roaming Services Agreements.  Each
               --------------------------------------------------
Intercarrier Roaming Services Agreement, as may be amended with respect to
Tritel 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. AWS will use commercially reasonable efforts to give Tritel written
notice 30 days in advance (or as promptly as reasonably practicable) prior to
               ----------
any such termination or expiration. Nothing in this Agreement obligates AWS to
enter into or to continue any Intercarrier Roaming Services Agreement with any
Other Wireless Carrier.

          1.4  Fraud Control  Tritel 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 call validation functions.

                                      -4-
<PAGE>

          1.5  Allocation of Roamer Revenues and Roamer Expenses.  AWS will
               -------------------------------------------------
treat Tritel as an affiliate of AWS for administrative purposes in collecting
and paying amounts owed to Tritel and owed by Tritel under the applicable
Intercarrier Roaming Services Agreement. Tritel acknowledges and agrees that
amounts owed to Tritel from Other Wireless Carriers will be collected by AWS,
intermingled with other funds owed to AWS and then distributed to Tritel based
upon the amounts owed to Tritel for Roamer usage by subscribers of the Other
Wireless Carriers. Tritel further acknowledges and agrees that AWS will make
payments for Tritel to Other Wireless Carriers based on the reports of Roamer
usage by subscribers of Tritel 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 Tritel,
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 30
days' written notice to Tritel.

          2.1  Effect of EDS PCC Agreement.  Tritel 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 Roaming Administration Services will cease. AWS will give
Tritel 30 days' prior notice of any cessation of Roaming Administration Services
under this section 2.1. Nothing in this Agreement obligates AWS to extend,
continue or enter into a new EDS PCC Agreement. Tritel 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.  Tritel 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 Tritel. Amounts owed each month for Fees and
Expenses will be included as amounts owed to AWS in the NSS function described
in Exhibit B.

     3.   Taxes.  Unless Tritel provides a certificate of exemption or other
          -----
evidence acceptable to appropriate taxing authorities, Tritel 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 Tritel under the Intercarrier Roaming Services Agreements
and (b) providing the Roaming Administration Services to Tritel. Such taxes will
be included in bills when imposed or required by law and shall be paid by Tritel
in accordance with this Agreement.

                                      -5-
<PAGE>

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

          4.1  Amounts Owed to AWS.  Tritel 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 Tritel has received the bill for such amounts at least five (5)
business days prior to such payment date. If Tritel receives the bill later than
such time, Tritel shall pay the bill within ten (10) days of its receipt by
Tritel. Payments will be submitted to: AT&T Wireless Services, Inc., 5000
Carillon Point, Kirkland, WA 98033, Attn: Billing and Intercarrier Settlement
Services.

          4.2  Amounts Owed to Tritel. AWS will pay Tritel in full any
               -----------------------
undisputed amounts owed to Tritel after the NSS procedure described in Exhibit B
has occurred on or before the fifteenth day of the month immediately following
the close of a Settlement Period.  Payments will be submitted to:

          Tritel Communications, Inc.
          1080 River Oaks Drive
          Suite B-100
          Jackson, MS 39208
          Attn: Revenue Director

          4.3  Time  Tritel acknowledges and understands that, AWS will pay
               ----
Other Wireless Carriers for Tritel's subscribers' roaming usage prior to
receiving payment from Tritel. Accordingly, Tritel 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. Tritel is strictly liable to make timely payments hereunder, and such
liability is not relieved by any dispute that Tritel 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 to, enhancements to billing systems.
Tritel will maintain compatibility with these systems and system enhancements,
including but not limited to the CIBER format for billing records. Tritel will
be responsible for the costs and expenses it incurs in maintaining this
compatibility.

                                      -6-
<PAGE>

     6.   Indemnification.  Tritel 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 Tritel or any subscriber of Tritel, 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 Tritel'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 Tritel 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 Tritel or its representatives, (e) a
breach by Tritel of any provision of this Agreement, or (f) a breach by Tritel
of any obligation to or agreement with its subscribers.

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

          7.1  AWS SHALL NOT BE RESPONSIBLE TO TRITEL 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, TRITEL
ACKNOWLEDGES THAT IN PERFORMING ITS OBLIGATIONS HEREUNDER AWS WILL RELY UPON
INFORMATION AND REPORTS PROVIDED TO AWS BY THIRD PARTIES. TRITEL 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 TRITEL, IN THE AGGREGATE, EXCEED THE AMOUNT
PAID IN FEES BY TRITEL 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 labor dispute in any manner
which is deemed by that party to be less than totally advantageous, in that
party's sole discretion.

                                      -7-
<PAGE>

     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,
Tritel 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 of the following reasons:

               9.2.1  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;

               9.2.2  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;

               9.2.3  By AWS with respect to any Intercarrier Roaming Services
Agreement or the EDS PCC Agreement in the event the applicable agreement expires
or terminates. The current EDS PCC Agreement expires on March 31, 2000, with
respect to settlement services and on June 30, 1999, with respect to call
validation services.

               9.2.4  By AWS immediately in the event that Tritel is no longer a
member in good standing with the NACN.

               9.2.5  By AWS with respect to the Roaming Administration Services
as set forth in Section 2.1 above.

          9.3  Either party may terminate this Agreement for any reason or for
no reason upon one hundred eighty (180) days prior written notice to the other
party.

     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.

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

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

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

                                      -9-
<PAGE>

          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
          5000 Carillon Point
          Kirkland, WA 98033
          Attn: Eric Baxter

          With a copy to:

          AT&T Wireless Services, Inc.
          5000 Carillon Point
          Kirkland, WA 98033
          Attn: Legal Department.

          If to Tritel

          Tritel Communications, Inc.
          1080 River Oaks Drive
          Suite B-100
          Jackson, MS 39208
          Attn: Revenue Director

          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.

                                      -10-
<PAGE>

          Tritel Customer Care Contact

          Name: Judy Varney
          Tel:  601-936-4140
          Fax:  601-936-6045

          TRITEL Roaming Services Contact

          Name: Cheryl McCullouch
          Tel:  601-936-4140
          Fax:  601-936-7752

          AWS Roamer Admin/Carrier Updates

          Name: David Mansisidor
                16221 NE 72nd Way
                Redmond, WA 98052

                                      -11-
<PAGE>

          AWS Finance/Accounting Contact

          Name: Ingrid Onstad
                16221 NE 72nd Way
                Redmond, WA 98052


          AWS Partnership Roaming Services Contact

          Name: Karla Essig
                16221 NE 72nd Way
                Redmond, WA 98052
                Tel: 425-580-8316
                Fax: 425-580-8390

     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 Tritel. Neither of the parties shall have the
authority to accept legal process on behalf of the other party. Nothing herein
gives Tritel 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.

          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.

                                      -12-
<PAGE>

          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 Tritel. Tritel
acknowledges that AWS may subcontract any or all of its duties under this
Agreement to a third party.

          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.

          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-
<PAGE>

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

                 13.12.1  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.

                 13.12.2  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.

                 13.12.3  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.

                 13.12.4  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 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

                                      -14-
<PAGE>

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.

                 13.12.5  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.

                                      -15-
<PAGE>

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


AWS:                     AT&T Wireless Services, Inc.



                         By ___________________________________
                         Its __________________________________


Tritel:                  Tritel, Inc



                         By ___________________________________
                         Its __________________________________
<PAGE>

                                   EXHIBIT A

                                 TRITEL System


                                    Ex. A-1
<PAGE>

                                  EXHIBIT A-1

                            Other Wireless Carriers

CARRIER SHORT NAME
------------------
360 DEGREES COMM.
AAT RSA COMPANY
AIR TOUCH CELLULAR
AIRTOUCH GREAT LAKES
ALLEGAN CELLULAR
ALLTEL
AMAR. CELL TEL
AMERICAN RURAL CELLULAR
AMERITECH
APPALACHIAN CELLULAR
ARCTIC SLOPE CELLULAR
ATLANTIC CELLULAR
AWS
BAKERSFIELD
BAY AREA
BELLSOUTH CELLULAR
BELLSOUTH MOBILITY
BLACKWATER CELLULAR
BLUE MOUNTAIN CELLULAR
BOSTON CELL ONE
C-1 COLUMBUS
C-1 EAST CENTRAL ILLINOIS
C-1 FINGER LAKES
C-1 FREDERICK
C-1 GREAT LAKES OF IOWA
C-1 HONOLULU
C-1 LAKE CHARLES
C-1 NE COLORADO
C-1 S. WI & N. IL
C-1 SENATOBIA
C-1 SW FLORIDA
C-1 WASH/BALT
CAL-ONE CELLULAR
CANTEL
CCPR
CELLULAR 2000/MN
CELLULAR ONE - FRONTIER

                                   Ex. A-1-1
<PAGE>

CHICAGO CELL 1
CITIZENS MOHAVE CELL
COASTEL COMMUNICATIONS
COMCAST CELLULAR
COMMNET CELLULAR INC
CONTEL/GTE
DCS OF KS/MO
DOBSON CELLULAR
EASTERBROOKE CELLULAR
ENID CELLULAR
GAIA, INC
GTE MOBILNET
HIGHLAND CELLULAR
HLD CELLULAR
HOUSTON CELL.
KAPLAN TELEPHONE
KINI
L.A.CELLULAR
LAKE HURON CELLULAR
MERCURY CELLULAR
MERCURY COMMUNICATIONS
METACOMM CELLULAR
MISSISSIPPI 34 CELLULAR
NEW VECTOR
NEW YORK / SWB
NEW YORK/ SWB
NEW YORK/SWB
PACE COMMUNICATIONS
PALMER WIRELESS
PETROCOM
PRICELLULAR
PRIME CELL-TX#9
SANTA CRUZ CELL.
SNET CELLULAR
SWB
SYGNET COMM INC.
SYRACUSE/UTICA
U.S. CELLULAR
UNION TELEPHONE
UNITEL INC.
VALLEY TELECOMMUNICATIONS
VANGUARD
W. ALABAMA CELLULAR

                                   Ex. A-1-2
<PAGE>

WESTEL
WESTERN WIRELESS

                                  Ex. A.1-3
<PAGE>

                                   EXHIBIT B

                        Roaming Administration Services

1.   Administration Services (AS)
     ----------------------------

     The AS will include various services that AWS will perform to manage
Tritel'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 Tritel
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 Tritel
pursuant to the Intercarrier Roamer Services Agreement between AWS and Tritel
that will enable Tritel's subscribers to roam in the markets owned by Other
Wireless Carriers.  Further, AWS shall provide Tritel with information
(including, without limitation, NPA/NXX combinations and MINs) provided 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 on Exhibit A-1.

     1.3  Outcollect Table Maintenance.  In the event that Tritel uses CONVERGYS
          -----------------------------
as its billing vendor, AWS will for a monthly fee maintain the Macro/Cell tables
necessary to bill subscribers of AWS and Other Wireless Carriers for use of the
Tritel 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 Tritel, 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  Tritel 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
Tritel. 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. Fraud brownout data will be archived for a period of twelve months
from the request date.

                                    Ex. B-1
<PAGE>

     1.5  Rate Monitoring  AWS will monitor roaming rates charged to Tritel and
          ---------------
roaming rates charged by Tritel. If an incorrect roaming rate is charged by
Tritel 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 and Tritel
will reimburse AWS for these amounts in the NSS process.  If an incorrect
roaming rate is charged to Tritel 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 greater than $200.  AWS will include any amounts received from
Other Wireless Carriers in Tritel's account in the NSS process. AWS shall not be
responsible for any amounts undercharged by AWS on behalf of Tritel to any Other
Wireless Carrier.

2.   Full Visibility (FV) Services
     -----------------------------

     FV services are an adjunct to validation service.  FV provides a mechanism
for receiving transaction information on all call attempts made by a Roamer who
subscribers to a carrier using validation services 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 validation services 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 validation services
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/NX range or by SID/BID
within a 45-day period.

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

3.   Intercarrier Settlement Services (ISS)
     --------------------------------------

     With ISS, AWS will instruct EDS PCC to edit Tritel's roaming records to
verify the billable status of these records. These edits will be performed in
accordance with the then

                                    Ex. B-2
<PAGE>

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 (noted below) will be returned to the serving carrier.

          3.1.1   Negative File Edit
          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 Message Edit
          3.1.9   Invalid Record Type per terms of Roamer Agreement Edit
          3.1.10  Incorrect agreed upon rate Edit
          3.1.11  Additional edits per CIBER standard Table 3

     3.2  Negative File Suppression Management.  Management of the clearinghouse
          ------------------------------------
negative file suppression edit will be performed by AWS and will be made in
accordance with current Intercarrier Roaming Services Agreements.

     3.3  Reports.  The Financial Reports as defined in Section 6.1 reflect
          -------
activity within a settlement cycle.  Each report is produced  at the end of each
settlement  cycle (the 16/th/ through the 15/th/ of the calendar month). Bi-
weekly reports from the 1/st/ through the 15/th/ and the 16/th/ through the end
of the month.

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

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

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

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

                                    Ex. B-3
<PAGE>

Incollect Obligations, Fees and Expenses with respect to AWS or any Other
Wireless Carrier, AWS shall pay such net Outcollect Obligations to Tritel as
described in Section 4.2 of this Agreement.

     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
Tritel for Roamer fraud incurred by Other Wireless Carriers and make payments to
Other Wireless Carriers for these invoices and add such amounts in the monthly
NSS process.  Information to be included in any invoice to AWS or an Other
Wireless Carrier must be in the format required by AWS, as that format may
change from time to time.  This information must be submitted to AWS within
forty five days 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 Tritel with the ability to validate the
billing status of Roamers from Other Wireless Carriers not connected with Tritel
through the NACN or other network of carriers. This verification will be
accomplished through comparison of the Roamer's MIN and ESN combination with a
database designed to identify potential fraudulent use.  This information can be
used by Tritel to deny service to callers when roaming in the TRITEL System.

6.   AWS Monthly Standard Reporting Package
     --------------------------------------

     6.1  Financial Reports.  These reports will be generated by the AWS
          -----------------
Financial Accounting group and will be provided to Tritel on a monthly basis.
The reports are:

     Invoice of Roamer Accounting
     RIMS Reports
     RIMS Financial G/L information
     Miscellaneous payment and receipts.

     6.2  Roamer Administration Reports.  These reports will be generated by AWS
          -----------------------------
Roamer Operations and sent bi-weekly to Tritel. The reports are:

Technical Data Coversheet           NPA/NXX Change
Technical Data Report               1900 NPA/NXX Change
Incollect and Outcollect Status     Billing Change
New PCS Build/Billing Change
NACN Change                         NACN Market Master
NACN Master                         NACN Market Change
NACN Switch Change                  AWS New Build PCS Switch change
NACN Switch Master                  OTMS Billing Report

                                    Ex. B-4
<PAGE>

Full Non-NACN Markets NPA/NXX      OTMS Billing Exception Reports

7.   Point of Contact for Industry Issues.
     ------------------------------------

     AWS, through its Vendor Management team, will consult with Tritel on issues
related to vendor user groups, the wireless industry on roaming issues, and
standards development on roaming issues.

8.   Telephone Support.
     -----------------

     8.1  Telephone Support.
          -----------------

     AWS will be available for one teleconference per month, lasting no more
than one hour, to review the services provided by AWS under this Agreement
during the prior Settlement Period.  In the event that Tritel uses more than one
hour per month of telephone support time, AWS may either (a) cease telephone
support at any time after the hour has been used or (b) charge Tritel $100.00
per hour for the telephone support time used in excess of one hour during the
month. AWS acknowledges and agrees that the one hour limitation does not apply
to telephone support in the ordinary course of business in performing the
services described in Section 1.2, 1.3, 1.4, or 3.2 of this Exhibit B.

                                    Ex. B-5
<PAGE>

                                   EXHIBIT C

                               Fees and Expenses

Service                              Fee
-------                              ---

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

XLI Transaction Fee (optional)       $0.16 per unique ESN validation per each
                                     calendar day.
                                     $1,000.00 per SID/BID minimum (waived if
                                     transaction charges are greater than or
                                     equal to $1,000.00).

FULL VISABILITY (optional)           $0.025/transaction
                                     $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: $2,000.00 per
                                     SID/BID flat fee and no record fee.
                                     Greater than 100K records monthly:
                                     $1,000.00 per SID/BID plus record fee for
                                     records above 100K. Monthly minimum shall
                                     not exceed $20,000.00 per month in 1999.

OUTCOLLECT TABLE MAINTENANCE         $50.00 per SID/BID per month
                                     $1,000.00 SID/BID set up fee.

CLEARINGHOUSE SET UP FEE             $1,000.00 per SID/BID

SS7 CONNECTION FEE                   $3,500.00 per Tritel switch/HLR
(non-NACN)

ROAM AGREEMENT                       $25,000.00
SET UP FEE

                                   Ex. C-1
<PAGE>

CIBERNET Fees                        $.005 per outcollect dollar owed to Tritel

Special Processing and Reports       As agreed by the parties in writing

Clearinghouse Financial Reports
(optional)                           $50.00 per market per report. (EDS paper
                                     reports)

Reports via diskette                 $100.00 per month (one set of reports per
                                     Month).

Tritel 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
Tritel 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.

                                    Ex. C-2