<PAGE>   1
                                                                   EXHIBIT 10.13

                                [ILLUMINET LOGO]

                            MASTER SERVICE AGREEMENT


<PAGE>   2

                            MASTER SERVICE AGREEMENT

                                TABLE OF CONTENTS

<TABLE>
<CAPTION>
SECTION        TITLE                                  PAGE
-------        -----                                  ----
<S>            <C>                                    <C>
I              Scope and Structure                      2
II             Compensation                             3
III            Proprietary Information                  3
IV             Resolution of Disputes                   4
V              Successors and Assigns                   5
VI             Independent Contractors                  6
VII            Indemnification                          6
VIII           Limitation of Liability                  7
IX             Year 2000 Compliance                     7
X              Compliance With Laws                     7
XI             Force Majeure                            8
XII            Amendments and Waivers                   8
XIII           Notices                                  9
XIV            Governing Law                            9
XV             Severability                             9
XVI            No Third Party Beneficiaries             9
XVII           Integration                              9
XVIII          Survival                                 9
XIX            Attorneys' Fees and Costs               10
XX             Headings                                10
XXI            Term                                    10
XXII           Execution In Counterparts               10
XXIII          Incorporation by Reference              11
Signatures                                             11
Attachment A   Participating Companies
</TABLE>



                                                                    Page 1 of 11
<PAGE>   3

      THIS MASTER SERVICE AGREEMENT, made and executed to be effective the day
and year set forth on the signature page of this Agreement, by and between
ILLUMINET, INC., a Delaware corporation ("ILLUMINET"), and the entities
identified on Attachment A annexed hereto, (individually referred to as
"Company" and collectively as "Companies").

W I T N E S S E T H:

        WHEREAS, ILLUMINET is a corporation which was formed by
telecommunications companies situated throughout the United States of America
and for several years has been providing database management, billing services,
general administrative services, revenue administration services, and other
services beneficial to the telecommunications industry; and

        WHEREAS, ILLUMINET operates a signaling network based on Signaling
System 7 ("SS7") protocol to effect the transport of data from and to the
switches of local exchange carriers and other services ("SIGNET 7(R)
Services"); and

        WHEREAS, the Company provides a variety of telecommunications services
to its subscribers and wishes to provide new and improved services utilizing
SIGNET 7(R) Services; and

        WHEREAS, in connection with the offering of SIGNET 7(R) Services,
ILLUMINET shall maintain an Independent Line Information Database ("Independent
LIDB") which will serve as the mechanism for the storage of database information
of all participants; and

        WHEREAS, the Company may participate in SIGNET 7(R) Services without
first upgrading its switch center to SS7 protocol, by providing line information
data to the Independent LIDB.

        NOW, THEREFORE, in consideration of the covenants and undertakings
herein contained and the mutual benefits to be derived herefrom, the adequacy of
which consideration is hereby acknowledged, ILLUMINET and the Company agree as
follows:

                         SECTION I: SCOPE AND STRUCTURE

        A. This Master Service Agreement specifies the general terms and
conditions pursuant to which ILLUMINET will perform certain services for the
Company. Additional terms and conditions pursuant to which the parties may
perform specific services or types of services will be set forth in "Modules"
that will be made and entered into by and between the parties, and upon the
execution of each such Module, shall be attached to and incorporated herein to
this Master Service Agreement and be subject to the terms and conditions of this
Master Service Agreement. Unless otherwise specified herein or implicit in the
context hereof, the term "Master Service Agreement" used herein shall include
any and all Modules hereto in effect from time to time.



                                                                    Page 2 of 11
<PAGE>   4

      B. Each Module incorporated in this Master Service Agreement shall contain
its own expiration and termination provisions and shall expire or terminate
individually in accordance with such provisions. This Master Service Agreement
shall remain in full force and effect in accordance with its terms from its
effective date until it expires or is terminated in accordance with the
provisions hereof, even if no Modules are in effect at any given time.

      C. In the event of any conflict or inconsistency between the provisions of
this Master Service Agreement (excluding Modules) and any individual Module of
this Master Service Agreement, the provisions of the Module shall control.

      D. ILLUMINET warrants that all services provided pursuant to this Master
Services Agreement, including all Modules hereunder, shall operate in
substantial accordance with ILLUMINET's corresponding User Guides, provided that
Company uses such services in substantial accordance with such User Guides.

                      SECTION II:   COMPENSATION

      The parties agree that the compensation to be paid by either party to the
other for services performed pursuant to this Master Service Agreement shall be
as specified in the applicable Module of this Master Service Agreement. Each
party agrees to pay the other party the compensation stated in each executed
Module, in accordance with all of the terms and conditions of such Module and
this Master Service Agreement. All payments made under this Master Service
Agreement shall be made in U.S. currency.

                SECTION III:   PROPRIETARY INFORMATION

      A. All information or other data relating to either party's business
activities which is disclosed by said party to the other party in connection
with this Master Service Agreement and/or any Module hereto, and designated as
proprietary or confidential information (hereinafter referred to as "Proprietary
Information") will be safeguarded and kept confidential by the other party to
the same extent that the other party protects its own proprietary and
confidential information, and shall be deemed the property of the disclosing
party. Such Proprietary Information in tangible form, and all reproductions
thereof, shall be returned to the disclosing party upon its request. The
receiving party shall not disclose or release any such Proprietary Information
without written authority from the disclosing party, to anyone other than an
employee, contractor, agent, attorney or affiliated company having a need for
such Proprietary Information in furtherance of the performance of services. The
receiving party shall require any



                                                                    Page 3 of 11
<PAGE>   5

person not its employee to whom it discloses or releases any such Proprietary
Information of the other party to sign an agreement to protect the
confidentiality of such Proprietary Information as provided in this Agreement,
prior to such disclosure or release.

        B. Upon the expiration or termination of this Master Service Agreement,
each party, at the request of the other party, shall promptly, but in any event
within thirty (30) days following the date of such request, return any and all
copies of Proprietary Information in tangible form, that such party received
from the other party and is still in its possession, custody, or control. In
addition, each party shall delete or erase all Proprietary Information from its
computer systems within the same time period and certify such compliance to the
other party in writing, signed by an officer of the certifying party. In the
event of the expiration or termination of a Module hereto, each party shall
return or eliminate any and all Proprietary Information in its possession,
custody, or control which pertains solely to such Module or the contract of
services covered by such Module, in the same manner and within the same time
period as provided above in this paragraph.

        C. The provisions of this Section III shall survive the termination or
expiration of this Master Service Agreement and any Module hereto for a period
of three (3) years unless otherwise agreed in writing by both parties.

        D. Notwithstanding any other provision of this Section III, neither
party hereto shall be required to return or to delete or erase from its computer
systems, any Proprietary Information or portion thereof which such party has
received pursuant to this Agreement and is required to retain among its records
by law or applicable regulations. In the event either party hereto is required
by law or regulation to retain Proprietary Information disclosed to it which the
other party has requested to be returned, the party so retaining the Proprietary
Information shall advise the disclosing party of that fact and of the law or
regulation requiring such retention, and all such retained Proprietary
Information shall continue to be maintained confidential as provided in this
Agreement and in the applicable provisions hereof which shall survive the
termination or expiration of this Agreement.

                       SECTION IV: RESOLUTION OF DISPUTES

        A. INFORMAL RESOLUTION. The parties agree that they shall attempt to
resolve any dispute regarding any right, obligation, duty, or liability arising
out of the provisions of this Master Service Agreement or any Module through
informal discussions or negotiations prior to resorting to formal dispute
resolution procedures contained in Subsection B below. If, at any



                                                                    Page 4 of 11
<PAGE>   6

time following the commencement of any such discussions or negotiations, either
party determines such discussions or negotiations are not likely to result in a
reasonable resolution of the dispute, it may send to the other party a written
statement of the issues or problems being discussed or negotiated. If the
dispute has not been resolved within sixty (60) days after the mailing of the
said statement of issues, either party shall have the right to serve a written
demand for arbitration upon the other and thereby commence binding arbitration
in accordance with the provisions set forth below. The mailing of the statement
of issues and the passage of sixty (60) days from the date of the mailing of
such statement of issues shall be conditions precedent to the commencement of
any arbitration proceedings hereunder.

        B. BINDING ARBITRATION. Within five (5) working days of delivery of a
demand, each party shall designate an arbitrator. The two designated arbitrators
shall then select a third arbitrator to complete the full arbitration panel
within twenty (20) working days, or as otherwise agreed.

              The arbitration panel shall commence hearing within sixty (60)
days of the selection of the panel. The scope of document production and the
enforcement of document requests may be ordered by the arbitrators to the extent
economical and reasonable. All discovery requests shall be subject to the
proprietary rights of the parties, and the arbitrators shall adopt procedures to
protect such rights. Except where contrary to the provisions set forth in this
Master Service Agreement, the rules of the American Arbitration Association
("AAA") shall be applied, provided, however, that the arbitration need not be
conducted under the auspices of the AAA, in which event the fee schedule of the
AAA shall not apply.

              All costs of arbitration and any award of attorney's fees shall be
awarded pursuant to the provisions of Section XIX of this Master Service
Agreement.

              Unless otherwise agreed in writing, the parties shall continue to
provide service under any Module, honor all commitments under this Master
Service Agreement, and continue to make payments in accordance with this Master
Service Agreement during the course of dispute resolution pursuant to the
provisions of this Section.

                        SECTION V: SUCCESSORS AND ASSIGNS

        This Agreement shall be binding upon and inure to the benefit of the
parties hereto and their respective successors and assigns; provided, however,
this Agreement shall not be assigned by either party hereto without the prior
written consent of the other party hereto, which consent shall not be
unreasonably withheld, except as provided in the next succeeding sentence. If
another corporation



                                                                    Page 5 of 11
<PAGE>   7

which is a parent, a wholly-owned or controlled subsidiary of a parent ("Sister
Company") or a wholly-owned or controlled subsidiary of one of the parties
hereto shall succeed to some or all of the business of the corporation which is
a party hereto, such party hereto may assign this Agreement to such parent,
subsidiary or Sister Company, without the consent of the other party, if such
parent, subsidiary or Sister Company shall expressly undertake in writing the
performance of the obligation and duties of the party hereto which it is
succeeding pursuant to such assignment. Notwithstanding any other provision in
this Agreement, Company may assign this Agreement, in whole or in part, to any
entity acquiring substantially all of the stock or assets of Company.

                       SECTION VI: INDEPENDENT CONTRACTORS

        Each party agrees that it shall perform its duties, obligations, and
services hereunder as an independent contractor and not as the employee or
servant of the other party. Except as expressly provided in any Module, neither
party nor any personnel employed or furnished by such party shall be deemed the
agent, employee, or servant of the other party or be entitled to any benefits
available under any plans for such other party's employees. Each party has and
hereby retains the right to exercise full control and supervision over the
performance of its obligations under this Master Service Agreement and retains
full control over the employment, supervision, direction, compensation, and
termination of all of its employees assisting in the performance of such
obligations. Each party shall be solely responsible for all matters relating to
the compensation of its respective employees, including payment of all
employment taxes and withholdings due in respect of its employees. Each party
shall be responsible for its acts and those of its employees during the
performance of such party's duties and obligations hereunder.

                          SECTION VII: INDEMNIFICATION

        The indemnification provisions of this Section shall apply to all
matters arising under this Master Service Agreement except that indemnification
or limitation of liability or related provisions contained in any Module to this
Master Service Agreement shall be controlling and take precedence over this
Section.

        To the extent not prohibited by law, each party shall indemnify the
other and hold it harmless against any loss, cost, claim, injury, or liability
relating to or arising out of negligence or willful misconduct by the
indemnifying party or its agents or contractors in connection with any services
or duties under this Master Service Agreement.



                                                                    Page 6 of 11
<PAGE>   8

        The indemnifying party under this Section agrees to defend any suit
brought against the other party for any such loss, cost, claim, injury, or
liability. Each party agrees to notify the other party promptly, in writing, of
any written claims, lawsuits, or demands for which the other party is
responsible under this Section and to cooperate in every reasonable way to
facilitate defense or settlement of claims. The indemnifying party shall not be
liable under this Section for settlement by the indemnified party of any claim,
lawsuit, or demand if the indemnifying party has not approved the settlement in
advance unless the indemnifying party has had the defense of the claim, lawsuit,
or demand tendered to it in writing and has failed to assume such defense.

        No claims under this Section, or claims with respect to charges under
this Master Service Agreement or adjustments to such charges, or any other
claims with respect to this Master Service Agreement, may be made more than two
(2) years (or such greater time as may be set by law) after the date of the
event that gave rise to the claim; provided, however, that claims for indemnity
under this Section may be made within two (2) years (or such greater time as may
be set by law) of the accrual of the cause of action for indemnity. The mailing
of a statement of issues as provided in Section IV.A hereinabove shall
constitute a claim with respect to this Master Service Agreement for the
purposes of satisfying the claims limitation period requirements of this Section
VII.

                      SECTION VIII: LIMITATION OF LIABILITY

        In no event shall either party be liable to the other party for
incidental, special, or consequential damages including but not limited to lost
profits.

                        SECTION IX: YEAR 2000 COMPLIANCE

        ILLUMINET represents and warrants that the software, hardware and
equipment that it uses to provide services under this Master Service Agreement
will record, store, process, and present calendar dates falling on or after
January 1, 2000, in the same manner, and with the same functionality, as
performed on or before December 31, 1999.

                         SECTION X: COMPLIANCE WITH LAWS

      Each party shall perform all of its obligations and undertakings set forth
in this Master Service Agreement in compliance with all applicable laws, orders,
and regulations specifically including, without limitation, all applicable laws,
orders, and regulations prohibiting



                                                                    Page 7 of 11
<PAGE>   9

discrimination against any employee or applicant for employment by
reason of race, color, religion, sex, national origin, age, or disability.

        In the event of any conflict between any provision of this Master
Service Agreement and any applicable law, order or regulation (including,
without limitation, any order, rule or regulation of any regulatory agency
having jurisdiction over the Company which may effect the matters covered by
this Master Service Agreement), the parties agree to negotiate in good faith,
such reasonable modification(s) as may be required to resolve such conflict.

                            SECTION XI: FORCE MAJEURE

        Neither party shall be held liable for any delay or failure of
performance of any part of this Master Service Agreement arising out of or
resulting from any cause beyond its control and without its fault or negligence,
including, without limitation, acts of God, acts or omissions of civil or
military authority, government regulations, embargoes, epidemics, war, terrorist
acts, riots, civil commotion or civil uprisings, insurrections, fires,
explosions, nuclear accidents, strikes, lockouts, power blackouts, earthquakes,
floods, hurricanes, tornados, volcanic actions, or other similar causes beyond
its control. If such delay or failure occurs, the non-delaying party may elect
to (a) terminate this Master Service Agreement or any Module thereof for
services not already received, if such Force Majeure condition results in a
delay or failure to perform which continues for more than thirty (30) days; or
(b) suspend such services for the duration of the delaying cause, obtain
elsewhere the services to be bought or sold hereunder, and resume performance
under this Master Service Agreement once the delaying cause ceases. Unless
written notice is given within thirty (30) days after such non-delaying party is
apprised of the delay or failure, (b) shall be deemed selected.

                       SECTION XII: AMENDMENTS AND WAIVERS

        This Master Service Agreement may be amended only by a written agreement
signed by both parties. No course of dealing or failure of either party to
enforce any provision of this Master Service Agreement shall be construed as a
waiver of such provision or of any other provision of this Master Service
Agreement. The amendment of any provision of this Master Service Agreement shall
not constitute an amendment or modification of any other part of this Master
Service Agreement unless expressly stated in such written agreement.



                                                                    Page 8 of 11
<PAGE>   10

                              SECTION XIII: NOTICES

        All written notices required under this Master Service Agreement shall
be given by telephonic facsimile transmission (FAX) or certified mail, return
receipt requested, addressed to such designated representative and address as
either party may from time to time provide by written notice to the other party,
and unless and until any further designation is made, such representative and
address for each party shall be as set forth on the signature page hereof.

                           SECTION XIV: GOVERNING LAW

        This Master Service Agreement shall be governed by and construed in
accordance with the laws of the State of Washington.

                            SECTION XV: SEVERABILITY

        In the event any provision of this Master Service Agreement shall be
held invalid or unenforceable by any Court of competent jurisdiction and if such
invalidity or unenforceability shall materially impair achieving the purpose and
intent of this Master Service Agreement, then this entire Master Service
Agreement shall be invalid and unenforceable. Otherwise, this Master Service
Agreement shall be construed as if not containing the particular provision or
provisions hereof held to be invalid or unenforceable, and the rights and
obligations of the parties shall be construed and enforced accordingly.

                    SECTION XVI: NO THIRD PARTY BENEFICIARIES

        This Master Service Agreement shall not be construed to provide any
third party with any remedy, claim, right of action, or other right.

                            SECTION XVII: INTEGRATION

        This Master Service Agreement constitutes the entire agreement between
the parties concerning the subject matter hereof. All representations,
statements, negotiations, understandings, proposals, and undertakings, whether
oral or in writing, with respect to the subject matter hereof are superseded and
replaced by this Master Service Agreement.

                             SECTION XVIII: SURVIVAL

        Any liability or obligation of either party to the other for acts or
omissions prior to the expiration or termination of this Master Service
Agreement or any part hereof, including, without



                                                                    Page 9 of 11
<PAGE>   11

limitation, either party's obligation to make payment for services rendered
prior to the effective date of such expiration or termination, and the
obligations of each party regarding the protection of Proprietary Information
shall survive the expiration or termination of this Master Service Agreement or
any part hereof.

                     SECTION XIX: ATTORNEYS' FEES AND COSTS

        In the event binding arbitration is commenced by either party to enforce
any covenant or undertaking of this Master Service Agreement, the prevailing
party in such arbitration shall be entitled to recover all reasonable costs and
expenses incurred in connection with such arbitration, including, without
limitation, costs of arbitration and a reasonable attorney's fee, and all such
sums shall be included in any ruling entered in said arbitration.

                              SECTION XX: HEADINGS

        The headings in this Master Service Agreement have been inserted for
convenience only and are not to be considered a part hereof and shall in no way
be construed to define or limit any of the terms herein or affect the meaning or
interpretation of any of the provisions of this Master Service Agreement.

                                SECTION XXI: TERM

        This Master Service Agreement shall continue in full force and effect
from the Effective Date until terminated by either party pursuant to written
notice delivered by the terminating party to the other party, not less than
ninety (90) days prior to the intended termination date. Notwithstanding the
foregoing sentence, this Master Service Agreement shall continue in full force
and effect for so long as any Module hereto is in effect, and this Master
Service Agreement may not be terminated pursuant to the foregoing sentence
unless any Module in effect at a given time, may, by its terms, also be
terminated at such time.

                     SECTION XXII: EXECUTION IN COUNTERPARTS

        This Master Service Agreement or any part hereof may be executed in any
number of counterparts, each of which shall be an original, but such
counterparts shall together constitute but one and the same instrument.

                                                                   Page 10 of 11
<PAGE>   12

                    SECTION XXIII: INCORPORATION BY REFERENCE

        Attachment A annexed hereto is, respectively by each and every reference
thereto incorporated herein as though fully set forth herein.

                                      # # #

        IN WITNESS WHEREOF, each of the parties hereto has made and caused this
Master Service Agreement, to be duly executed for it and on its behalf by its
authorized representative, to be effective the date of the last signature below
(the "Effective Date").

        Note: The signatories to this Agreement hereby warrant and represent
that they have the authority to execute this Agreement on behalf of the entity
or entities for which they sign.

                                       ILLUMINET, INC.

March 29,1999                          By: /s/ RICHARD R. WOLF
-----------------------------------       ------------------------------------
Date Signed                            Richard R. Wolf
                                       Director, Legal and Regulatory Affairs

                                       ILLUMINET ADDRESS:
                                       Illuminet, Inc.
                                       4501 Intelco Loop SE
                                       Lacey, WA  98503

                                                                     "ILLUMINET"

                                       EACH COMPANY IDENTIFIED ON
                                       ATTACHMENT "A" ATTACHED HERETO

3/25/99                                By: /s/ MICHAEL BLACK
-----------------------------------       ------------------------------------
Date Signed                            Its Authorized Representative

                                       Michael Black
                                       ---------------------------------------
                                       Printed Name of Signatory

                                       Senior VP
                                       ---------------------------------------
                                       Title of Signatory

                                                                       "COMPANY"



                                                                   Page 11 of 11
<PAGE>   13

                                  ATTACHMENT A
                                       TO
                            MASTER SERVICE AGREEMENT

                             PARTICIPATING COMPANIES

<TABLE>
<CAPTION>
                                        (ILLUMINET
                                         COMPLETES)
COMPLETE LEGAL NAME AND                  EFFECTIVE        STATE OF         LOCATED IN
ADDRESS OF PARTICIPATING COMPANY           DATE         INCORPORATION       (STATE)              OCN
--------------------------------           ----         -------------       -------              ---
<S>                                     <C>             <C>                <C>                  <C>
Advanced Tel Com Group, Inc.                              Delaware         California           4268
100 Stony Point Rd. Suite 130                                              applies to
Santa Rosa, CA 95401                                                       all States

Advanced Tel Com Group, Inc.                              Delaware         California           4296
100 Stony Point Rd. Suite 130                                                (only)
Santa Rosa, CA 95401

Advanced Tel Com Group, Inc.                              Delaware           Oregon             4271
100 Stony Point Rd. Suite 130                                                (only)
Santa Rosa, CA 95401

Advanced Tel Com Group, Inc.                              Delaware         Washington           4272
100 Stony Point Rd. Suite 130                                                (only)
Santa Rosa, CA 95401
</TABLE>

                                                                     Page 1 of 1