Document:

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                                                                     Exhibit 4.2

                               Escrow Agreement

                                (General Form)

          THIS ESCROW AGREEMENT (as the same may be amended or modified from
time to time by mutual agreement of the parties and including any and all
written instructions given to "Escrow Agent" (hereinafter defined) pursuant
hereto, this "Escrow Agreement") is made and entered into as of June 6, 2000 by
and among American TeleSource International, Inc., a Delaware corporation
("Party A"), COMSAT Mexico, S.A. de C.V., a Mexican corporation ("Party B", and
together with Party A, sometimes referred to collectively as the "Other
Parties"), and CHASE BANK OF TEXAS, NATIONAL ASSOCIATION, a national banking
association with its principal offices in Houston, Harris County, Texas (the
"Bank").

                             W I T N E S S E T H :

                                   RECITALS

          WHEREAS, Party B desires to sell 266,321 shares of Grupo Intelcom de
Mexico, S.A. de C.V. (the "Shares") to Party A, and Party A desires to purchase
the Shares from Party B in accordance with the terms and conditions set forth in
that Agreement for the Sale and Purchase of Part of the Issued Share Capital of
Grupo Intelcom de Mexico, S.A. de C.V. dated effective June 6, 2000;

          WHEREAS, Party A and Party B wish the Shares and a portion of the
purchase price for the shares to be held in escrow pending the resolution of
certain contingencies.

          Whereas, Party A and Party B have requested Bank to act in the
capacity of escrow agent under this Escrow Agreement, and Bank, subject to the
terms and conditions hereof, has agreed to do so.

          Now, Therefore, in consideration of the premises and mutual covenants
and agreements contained herein, the parties hereto hereby agree as follows:

          1.   Appointment of Escrow Agent. Each of Party A and Party B
hereby appoints the Bank as the escrow agent under this Escrow Agreement (the
Bank in such capacity, the "Escrow Agent"), and Escrow Agent hereby accepts such
appointment.

         2.    Deposit. Upon execution of this Escrow Agreement, Party A will
deliver to the Escrow Agent the sum of Seventy Five Thousand U.S. Dollars
($75,000.00) (as said amount may increase or decrease as a result of the
investment and reinvestment thereof, the "Deposit"), and Party B will deliver to
the Escrow Agent duly executed transfers of the Shares (the "Share Transfer
Evidence") to be held by Escrow Agent in accordance with the terms hereof.
Subject to and in accordance with the terms and conditions hereof, Escrow Agent
agrees that it shall receive, hold in escrow, invest and reinvest and release or
distribute the Deposit. It is hereby expressly stipulated and agreed that all
interest and other earnings on the Deposit shall become a part of the Deposit
for all purposes. The parties agree that Party A will determine if the Share
Transfer Evidence is acceptable to Party A prior to deposit of the Share
Transfer Evidence with the Bank, and that Bank

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shall have no responsibility whatsoever to determine if the Share Transfer
Evidence is valid, sufficient, or otherwise acceptable.

          3.   Investment of the Deposit. Escrow Agent shall invest and reinvest
the Deposit in the United States Treasury Bills with a maturity of thirty days
or less unless otherwise instructed in writing by Party B. Such written
instructions, if any, referred to in the foregoing sentence shall specify the
type and identity of the investments to be purchased and/or sold and shall also
include the name of the broker-dealer, if any, which Party B directs the Escrow
Agent to use in respect of such investment, any particular settlement procedures
required, if any (which settlement procedures shall be consistent with industry
standards and practices), and such other information as Escrow Agent may
require. Escrow Agent shall not be liable for failure to invest or reinvest
funds absent sufficient written direction. Unless Escrow Agent is otherwise
directed in such written instructions, Escrow Agent may use a broker-dealer of
its own selection, including a broker-dealer owned by or affiliated with Escrow
Agent or any of its affiliates. The Escrow Agent or any of its affiliates may
receive compensation with respect to any investment directed hereunder. It is
expressly agreed and understood by the parties hereto that Escrow Agent shall
not in any way whatsoever be liable for losses on any investments, including,
but not limited to, losses from market risks due to premature liquidation or
resulting from other actions taken pursuant to this Escrow Agreement.

          Receipt, investment and reinvestment of the Deposit shall be confirmed
by Escrow Agent as soon as practicable by account statement, and any
discrepancies in any such account statement shall be noted by Party B to Escrow
Agent within 30 calendar days after receipt thereof. Failure to inform Escrow
Agent in writing of any discrepancies in any such account statement within said
30-day period shall conclusively be deemed confirmation of such account
statement in its entirety. For purposes of this paragraph, (a) each account
statement shall be deemed to have been received by the party to whom directed on
the earlier to occur of (i) actual receipt thereof and (ii) three "Business
Days" (hereinafter defined) after the deposit thereof in the United States Mail,
postage prepaid and (b) the term "Business Day" shall mean any day of the year,
excluding Saturday, Sunday and any other day on which national banks are
required or authorized to close in Houston, Texas.

          4.   Disbursement of Deposit.  Escrow Agent is hereby authorized to
make disbursements of the Deposit only as follows:

                    (a)  the Escrow Agent receives a Release of Escrow attached
          as Exhibit A executed by each of Party A and Party B, in which case
             ---------
          the Escrow Agent shall deliver the Share Transfer Evidence to Party A
          via overnight mail to the address provided in Section 13, below, and
          shall disburse the Deposit to Party B as directed in writing by Party
          B;

                    (b)  the Escrow Agent receives after the Escrow Termination
          Date, as defined below, the Termination of Escrow attached as Exhibit
                                                                        -------
          B, executed by either of Party A or Party B, in which case the Escrow
          -
          Agent shall deliver the Share Transfer Evidence to Party B to the
          address provided in Section 13, below, and the Deposit to Party A as
          directed in writing by Party A; The "Escrow Termination Date" shall be
          September 30, 2000 or such later date specified by the parties in a
          joint instruction to the Escrow Agent in form and substance
          satisfactory to Escrow Agent.

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                    (c)  As permitted by this Escrow Agreement, to Escrow Agent;
          and

                    (d)  Into the registry of the court in accordance with
          Sections 8 or 15 hereof.

          5.   Tax Matters. Party A and Party B shall provide Escrow Agent
with its taxpayer identification number documented by an appropriate Form W 8 or
Form W 9 upon execution of this Escrow Agreement. Failure so to provide such
forms may prevent or delay disbursements from the Deposit and may also result in
the assessment of a penalty and Escrow Agent's being required to withhold tax on
any interest or other income earned on the Deposit. Any payments of income shall
be subject to applicable withholding regulations then in force in the United
States or any other jurisdiction, as applicable.

          6.   Scope of Undertaking.  Escrow Agent's duties and responsibilities
in connection with this Escrow Agreement shall be purely ministerial and shall
be limited to those expressly set forth in this Escrow Agreement. Escrow Agent
is not a principal, participant or beneficiary in any transaction underlying
this Escrow Agreement and shall have no duty to inquire beyond the terms and
provisions hereof. Escrow Agent shall have no responsibility or obligation of
any kind in connection with this Escrow Agreement or the Deposit and shall not
be required to deliver the Deposit or any part thereof or take any action with
respect to any matters that might arise in connection therewith, other than to
receive, hold, invest, reinvest and deliver the Deposit as herein provided.
Without limiting the generality of the foregoing, it is hereby expressly agreed
and stipulated by the parties hereto that Escrow Agent shall not be required to
exercise any discretion hereunder and shall have no investment or management
responsibility and, accordingly, shall have no duty to, or liability for its
failure to, provide investment recommendations or investment advice to the Other
Parties or either of them. Escrow Agent shall not be liable for any error in
judgment, any act or omission, any mistake of law or fact, or for anything it
may do or refrain from doing in connection herewith, except for, subject to
Section 7 hereinbelow, its own willful misconduct or gross negligence. It is the
intention of the parties hereto that Escrow Agent shall never be required to
use, advance or risk its own funds or otherwise incur financial liability in the
performance of any of its duties or the exercise of any of its rights and powers
hereunder.

          7.   Reliance; Liability.  Escrow Agent may rely on, and shall not
be liable for acting or refraining from acting in accordance with, any written
notice, instruction or request or other paper furnished to it hereunder or
pursuant hereto and believed by it to have been signed or presented by the
proper party or parties. Escrow Agent shall be responsible for holding,
investing, reinvesting and disbursing the Deposit pursuant to this Escrow
Agreement; provided, however, that in no event shall Escrow Agent be liable for
any lost profits, lost savings or other special, exemplary, consequential or
incidental damages in excess of Escrow Agent's fee hereunder and provided,
further, that Escrow Agent shall have no liability for any loss arising from any
cause beyond its control, including, but not limited to, the following: (a) acts
of God, force majeure, including, without limitation, war (whether or not
declared or existing), revolution, insurrection, riot, civil commotion,
accident, fire, explosion, stoppage of labor, strikes and other differences with
employees; (b) the act, failure or neglect of any Other Party or any agent or
correspondent or any other person selected by Escrow Agent; (c) any delay,
error, omission or default of any mail, courier, telegraph, cable or wireless
agency or operator; or (d) the acts or edicts of any government or governmental
agency or other group or entity exercising governmental powers. Escrow Agent is
not responsible or liable in any manner whatsoever for the sufficiency,
correctness, genuineness or validity of the subject matter of this Escrow
Agreement or any part hereof or for the transaction or transactions requiring or
underlying the execution of this Escrow Agreement, the form or execution

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hereof or for the identity or authority of any person executing this Escrow
Agreement or any part hereof or depositing the Deposit.

          8.   Right of Interpleader.  Should any controversy arise involving
the parties hereto or any of them or any other person, firm or entity with
respect to this Escrow Agreement or the Deposit, or should a substitute escrow
agent fail to be designated as provided in Section 15 hereof, or if Escrow Agent
should be in doubt as to what action to take, Escrow Agent shall have the right,
but not the obligation, either to (a) withhold delivery of the Deposit until the
controversy is resolved, the conflicting demands are withdrawn or its doubt is
resolved or (b) institute a petition for interpleader in any court of competent
jurisdiction to determine the rights of the parties hereto. In the event Escrow
Agent is a party to any dispute, Escrow Agent shall have the additional right to
refer such controversy to binding arbitration. Should a petition for
interpleader be instituted, or should Escrow Agent be threatened with litigation
or become involved in litigation or binding arbitration in any manner whatsoever
in connection with this Escrow Agreement or the Deposit, the Other Parties
hereby jointly and severally agree to reimburse Escrow Agent for its attorneys'
fees and any and all other expenses, losses, costs and damages incurred by
Escrow Agent in connection with or resulting from such threatened or actual
litigation or arbitration prior to any disbursement hereunder.

          9.   Indemnification.  The Other Parties hereby jointly and severally
indemnify Escrow Agent, its officers, directors, partners, employees and agents
(each herein called an "Indemnified Party") against, and hold each Indemnified
Party harmless from, any and all expenses, including, without limitation,
attorneys' fees and court costs, losses, costs, damages and claims, including,
but not limited to, costs of investigation, litigation and arbitration, tax
liability and loss on investments suffered or incurred by any Indemnified Party
in connection with or arising from or out of this Escrow Agreement, except such
acts or omissions as may result from the willful misconduct or gross negligence
of such Indemnified Party. IT IS THE EXPRESS INTENT OF EACH OF PARTY A AND PARTY
B TO INDEMNIFY EACH OF THE INDEMNIFIED PARTIES FOR, AND HOLD THEM HARMLESS
AGAINST, THEIR OWN NEGLIGENT ACTS OR OMISSIONS.

          10.  Compensation and Reimbursement of Expenses.  Party A hereby
agrees to pay Escrow Agent for its services hereunder in accordance with Escrow
Agent's fee schedule as in effect from time to time and to pay all expenses
incurred by Escrow Agent in connection with the performance of its duties and
enforcement of its rights hereunder and otherwise in connection with the
preparation, operation, administration and enforcement of this Escrow Agreement,
including, without limitation, attorneys' fees, brokerage costs and related
expenses incurred by Escrow Agent.

          11.  Lien.  Party A hereby grants to Escrow Agent a lien upon, and
security interest in, all its right, title and interest in and to all of the
Share Transfer Evidence as security for the payment and performance of its
obligations owing to Escrow Agent hereunder, including, without limitation, its
obligations of payment, indemnity and reimbursement provided for hereunder,
which lien and security interest may be enforced by Escrow Agent without notice
by charging and setting-off and paying from, the Deposit any and all amounts
then owing to it pursuant to this Escrow Agreement or by appropriate foreclosure
proceedings.

          12.  Funds Transfer.  In the event funds transfer instructions are
given (other than in writing at the time of execution of the Agreement), whether
in writing, by telefax, or otherwise, the Escrow Agent is authorized to seek
confirmation of such instructions by telephone call-back to the person or person
designated on Schedule 1 hereto, and the Escrow Agent may rely upon the
confirmations of anyone purporting to be the person or persons so designated.
The persons and

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telephone numbers for call-backs may be changed only in writing actually
received and acknowledged by the Escrow Agent. The parties to this Agreement
acknowledge that such security procedure is commercially reasonable.

          It is understood that the Escrow Agent and the beneficiary's bank in
any funds transfer may rely solely upon any account numbers or similar
identifying number provided by either of the other parties hereto to identify
(i) the beneficiary, (ii) the beneficiary's bank, or (iii) an intermediary bank.
The Escrow Agent may apply any of the escrowed funds for any payment order it
executes using any such identifying number, even where its use may result in a
person other than the beneficiary being paid, or the transfer of funds to a bank
other than the beneficiary's bank or an intermediary bank, designated.

          13.  Notices.  Any notice or other communication required or
permitted to be given under this Escrow Agreement by any party hereto to any
other party hereto shall be considered as properly given if in writing and (a)
delivered against receipt therefor, (b) mailed by registered or certified mail,
return receipt requested and postage prepaid or (c) sent by telefax machine, in
each case to the address or telefax number, as the case may be, set forth below:

          If to Escrow Agent:
                            Chase Bank of Texas, National Association
                            600 Travis Street, Suite 1150
                            Houston, TX 77002
                            Attn: May Ng
                            CMFS/Escrow Section
                            Telefax No.:  (713)  216-6467
                            Telephone No.: (713) 216-6927

          If to Party A:    American TeleSource International, Inc.
                            12500 Network Blvd., Suite 407
                            San Antonio, Texas 78249
                            Attn:  Arthur L. Smith
                            Telefax:  (210)558-6095
                            Telephone: (210) 558-6090

         If to Party B:     COMSAT Mexico, S.A. de C.V.
                            Ave. Renato Leduc No. 321
                            Col. Toriello Guerra 14050
                            Mexico, D.F.
                            Attention:  Alfonso Torres Roqueni
                            Telefax: (525) 528-2321
                            Telephone:  (525) 528-2100

         with a copy to:    Office of the General Counsel
                            COMSAT International, Inc.
                            6560 Rock Spring Drive
                            Bethesda, Maryland  20817
                            Telefax: (301)214-7128
                            Telephone: (301)214-3611

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Except to the extent otherwise provided in the second paragraph of Section 3
hereinabove, delivery of any communication given in accordance herewith shall be
effective only upon actual receipt thereof by the party or parties to whom such
communication is directed. Any party to this Escrow Agreement may change the
address to which communications hereunder are to be directed by giving written
notice to the other party or parties hereto in the manner provided in this
section.

          14.  Consultation with Legal Counsel.  Escrow Agent may consult with
its counsel or other counsel satisfactory to it concerning any question relating
to its duties or responsibilities hereunder or otherwise in connection herewith
and shall not be liable for any action taken, suffered or omitted by it in good
faith upon the advice of such counsel.

          15. Choice of Laws; Cumulative Rights.  This Escrow Agreement shall be
construed under, and governed by, the laws of the State of Texas, excluding,
however, (a) its choice of law rules and (b) the portions of the Texas Trust
Code Sec. 111.001, et seq. of the Texas Property Code concerning fiduciary
duties and liabilities of trustees. All of Escrow Agent's rights hereunder are
cumulative of any other rights it may have at law, in equity or otherwise. The
parties hereto agree that the forum for resolution of any dispute arising under
this Escrow Agreement shall be Harris County, Texas, and each of the Other
Parties hereby consents, and submits itself, to the jurisdiction of any state or
federal court sitting in Harris County, Texas.

          16.  Resignation.  Escrow Agent may resign hereunder upon ten (10)
days' prior notice to the Other Parties. Upon the effective date of such
resignation, Escrow Agent shall deliver the Deposit to any substitute escrow
agent designated by Party A and Party B in writing. If Party A and Party B fail
to designate a substitute escrow agent within ten (10) days after the giving of
such notice, Escrow Agent may institute a petition for interpleader. Escrow
Agent's sole responsibility after such 10-day notice period expires shall be to
hold the Deposit (without any obligation to reinvest the same) and to deliver
the same to a designated substitute escrow agent, if any, or in accordance with
the directions of a final order or judgment of a court of competent
jurisdiction, at which time of delivery Escrow Agent's obligations hereunder
shall cease and terminate.

          17.  Assignment.  This Escrow Agreement shall not be assigned by
either of the Other Parties without the prior written consent of Escrow Agent
(such assigns of the Other Parties to which Escrow Agent consents, if any, and
Escrow Agent's assigns being hereinafter referred to collectively as "Permitted
Assigns").

          18.  Severability.  If one or more of the provisions hereof shall for
any reason be held to be invalid, illegal or unenforceable in any respect under
applicable law, such invalidity, illegality or unenforceability shall not affect
any other provisions hereof, and this Escrow Agreement shall be construed as if
such invalid, illegal or unenforceable provision had never been contained
herein, and the remaining provisions hereof shall be given full force and
effect.

          19.  Termination.  This Escrow Agreement shall terminate upon the
disbursement, in accordance with Sections 4 or 15 hereof, of the Deposit in
full; provided, however, that in the event all fee, expenses, costs and other
amounts required to be paid to Escrow Agent hereunder are not fully and finally
paid prior to termination, the provisions of Section 10 hereof shall survive the
termination hereof and, provided further, that the last two sentences of Section
8 hereof and the provisions of Section 9 hereof shall, in any event, survive the
termination hereof.

          20.  General.  The section headings contained in this Escrow Agreement
are for reference purposes only and shall not affect in any way the meaning or
interpretation of this Escrow

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Agreement. This Escrow Agreement and any affidavit, certificate, instrument,
agreement or other document required to be provided hereunder may be executed in
two or more counterparts, each of which shall be deemed an original, but all of
which taken together shall constitute but one and the same instrument. Unless
the context shall otherwise require, the singular shall include the plural and
vice-versa, and each pronoun in any gender shall include all other genders. The
terms and provisions of this Escrow Agreement constitute the entire agreement
among the parties hereto in respect of the subject matter hereof, and neither
the Other Parties nor Escrow Agent has relied on any representations or
agreements of the other, except as specifically set forth in this Escrow
Agreement. This Escrow Agreement or any provision hereof may be amended,
modified, waived or terminated only by written instrument duly signed by the
parties hereto. This Escrow Agreement shall inure to the benefit of, and be
binding upon, the parties hereto and their respective heirs, devisees,
executors, administrators, personal representatives, successors, trustees,
receivers and Permitted Assigns. This Escrow Agreement is for the sole and
exclusive benefit of the Other Parties and the Escrow Agent, and nothing in this
Escrow Agreement, express or implied, is intended to confer or shall be
construed as conferring upon any other person any rights, remedies or any other
type or types of benefits.

          In Witness Whereof, the parties hereto have executed this Escrow
Agreement to be effective as of the date first above written.

                 [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

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                                   American TeleSource International, Inc.

                                   By: /s/ Arthur L. Smith
                                       ---------------------------------------
                                   Name:   Arthur L. Smith
                                   Title:  Chief Executive Officer

                                                                       "Party A"

                                   COMSAT de Mexico, S.A. de C.V.

                                   By: /s/ Mary Gramaglia
                                       ---------------------------------------
                                       Mary Gramaglia
                                       Attorney-in-Fact

                                                                       "Party B"

                                   CHASE BANK OF TEXAS,
                                    NATIONAL ASSOCIATION

                                   By: _________________________________________
                                   Name:  ______________________________________
                                   Title:  _____________________________________
                                                                  "Escrow Agent"

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                                  Schedule 1

               Telephone Number(s) for Call-backs and Person(s)
               Designated to Confirm Funds Transfer Instructions

If to Party A:

          Name                                 Telephone Number
          ----                                 ----------------

1.    Alice L. King                            (210)558-6090

2.    Ray Martinez                             (210)558-6090

If to Party B:

Name                                           Telephone Number
----                                           ----------------

1.    Mary Gramaglia                           (310)214-3788

2.    Bob Myer                                 (310)214-3090

Telephone call-backs shall be made to either Party A or B if joint instructions
are required pursuant to the Escrow Agreement.

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                                   EXHIBIT A
                                   ---------

                               RELEASE OF ESCROW

re:  Escrow Agreement dated effective as of June 6, 2000 between COMSAT Mexico,
     S.A. de C.V., American TeleSource International, Inc., and Chase Bank of
     Texas, N.A. (the "Escrow Agreement").

Date:   ______________

     The undersigned party to the Escrow Agreement hereby states that the
party's conditions precedent to release of escrow specified in that Agreement
for the Sale and Purchase of Part of the Issued Share Capital of Grupo Intelcom
de Mexico, S.A. de C.V. dated effective June 6, 2000 have been satisfied, and
hereby directs the Escrow Agent, upon receipt of a Release of Escrow executed by
the other party to the Escrow Agreement to release the Deposit and the Share
Transfer Evidence as directed in Section 4(a) of the Escrow Agreement.

         AMERICAN TELESOURCE INTERNATIONAL, INC.

         By:      _________________________
                  Arthur L. Smith,
                  Chief Executive Officer

         COMSAT Mexico, S.A. de C.V.

         By:      _________________________
                  Mary Gramaglia
                  Attorney-in-Fact

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                                    EXHIBIT B
                                    ---------

                              TERMINATION OF ESCROW

re:  Escrow Agreement dated effective as of June 6, 2000 between COMSAT Mexico,
     S.A. de C.V., American TeleSource International, Inc., and Chase Bank of
     Texas, N.A. (the "Escrow Agreement").

Date:   ______________

     The undersigned party to the Escrow Agreement hereby states that the
party's conditions precedent to release of escrow specified in that Agreement
for the Sale and Purchase of Part of the Issued Share Capital of Grupo Intelcom
de Mexico, S.A. de C.V. dated effective June 6, 2000 have not been satisfied,
and hereby directs the Escrow Agent to release the Deposit and the Share
Transfer Evidence as directed in Section 4(b) of the Escrow Agreement.

         AMERICAN TELESOURCE INTERNATIONAL, INC.

         By:      _________________________
                  Arthur L. Smith,
                  Chief Executive Officer

or

         COMSAT Mexico, S.A. de C.V.

         By:      _________________________
                  Mary Gramaglia
                  Attorney-in-Fact

                                       11<PAGE>

                                                                     Exhibit 4.3
                                    Agreement

     This Agreement (this "Agreement") dated effective as of June 7, 2000 is
between Alfonso Torres Roqueni, an individual residing in Mexico City, Mexico
("Torres"), and American TeleSource International, Inc., a Delaware corporation
("ATSI").

                                    RECITALS

A.   Torres owns 51% of the stock of Grupo Intelcom de Mexico, S.A. de C.V., a
     Mexican corporation ("Grupo") (the "Grupo Stock)";

B.   Torres owns 99.9% of the stock of Telemarketing de Mexico, S.A. de C.V., a
     Mexican corporation ("Telemarketing") (the "Telemarketing Stock");

C.   Rodolfo Torres Roqueni ("RTorres") owns .1% of the stock of Telemarketing
     ("RTorresStock");

D.   ATSI has or will acquire 49% of the stock of Grupo from COMSAT Mexico, S.A.
     de C.V. ("COMSAT Mexico") contemporaneously with the transactions described
     in this Agreement, with that stock and part of the purchase price for that
     stock to be held in escrow pending the occurrence of certain conditions
     precedent defined in that Agreement for the Sale and Purchase Of Part of
     the Issued Share Capital of Grupo Intelcom de Mexico, S.A. de C.V. between
     ATSI and COMSAT Mexico dated June 6, 2000 (the "COMSAT Agreement");

E.   Torres desires to sell 3% of the shares of Grupo to ATSI's Partners, as
     defined below ("3%Stock") and ATSI desires the Partners to acquire the
     3%Stock;

F.   Torres desires to transfer control of his remaining 48% of the shares of
     Grupo ("48%Stock") to the Partners by causing RTorres to transfer the
     RTorresStock to a Partner; transferring the 48%Stock to Telemarketing as a
     capital increase, and refraining from exercising his preemptive right to
     subscribe and pay additional capital increases in Telemarketing such that
     the Partners are able to dilute his percentage ownership of Telemarketing;

G.   ATSI desires the Partners to obtain control of the 48%Stock in the manner
     described in paragraph F, above; and

H.   ATSI desires Torres to perform consulting services in connection with the
     transactions described above and Torres desires to perform those services.

  Therefore, for the consideration described and contained in this Agreement,
and on the terms and conditions described in this Agreement, the parties agree
as follows:

                                       1
<PAGE>

1.       Definitions.  The following terms shall have the meanings set forth
below:

     "ATSI Shares" means the First ATSI Shares and the Second ATSI Shares.

     "Business Day" shall mean a weekday on which the banks in neither the
     United States nor Mexico are required or permitted to be closed.

     "COFETEL" shall mean the Comision Federal de Telecomunicaciones.

     "COMSAT SCT Approval" shall have the meaning given in Section 2(b) of this
     Agreement.

     "Escrow Agent" shall mean the Laredo National Bank acting as Escrow Agent
     pursuant to that Escrow Agreement executed by ATSI and Torres and attached
     as Exhibit 1 to this Agreement.
        ---------

     "First ATSI Shares" shall mean the 50,000 shares of ATSI common stock
     described in Section 2(a)(1)(A)(i) of this Agreement.

     "First Release" and "First Release Date" shall have the meanings given them
     in Section 2(b) of this Agreement.

     "knowledge of" shall mean (i) in the case of natural person, the particular
     fact was known, or not known, as the context requires, to that person after
     diligent investigation and inquiry by that person, and (ii) in the case of
     an entity, the particular fact was known, or not known, as the context
     requires, to any employee of such entity after diligent investigation and
     inquiry by the principal executive officer of that entity.

     "Long Distance Concession" means that Concession issued on June 4, 1998 by
     the SCT to Grupo.

     "Minutes" shall have the meaning given them in Section 2(a)(2)(A)(iv).

     "Note" shall mean the Note attached as Exhibit 2(a)(1)(A)(ii) to this
                                            -------
     Agreement.

     "Partners" means Elvia Salas de De Stefano and Jesus Ricardo Enriquez
     Perez, or such other persons that may be designated by ATSI.

     "Poder General" shall have the meaning given in Section 2(a)(2)(A)(vi).

     "Second ATSI Shares" shall mean the 350,000 shares of ATSI common stock
     described in Section 2(b) of this Agreement.

                                       2
<PAGE>

     "Second Release" and "Second Release Date" shall have the meanings given in
     Section 2(c) of this Agreement.

     "SEC" shall mean the United States Securities and Exchange Commission.

     "SECOFI" shall mean the Secretaria de Comercio y Fomento Industrial.

     "Simultaneous Release" shall have the meaning given in Section 2(d) of this
     Agreement.

     "SRE" shall mean the Secretaria de Relaciones Exteriores.

     "SCT" shall mean the Secretaria de Comunicaciones y Transportes.

     "Telemarketing Stock Assignment" shall have the meaning given in Section
     2(a)(2)(A)(v) of this Agreement.

     "Torres Designee" shall mean the person or persons designated by Torres in
     writing to receive the ATSI Shares, the Note and the Warrant upon the First
     Release, Second Release, or Simultaneous Release, if applicable.

     "Telemarketing Capital Increase" means the approximately $70,000 and 00/100
     U.S. Dollars ($739,000 and 00/100 Pesos Currency of the United Mexican
     States) increase in Telemarketing's capital stock which was resolved on the
     General Extraordinary Shareholders' Meeting held on February 10 2000.

     "Warrant" shall mean the warrant for the purchase of ATSI common stock
     attached as Exhibit 2(a)(1)(A)(iii) to this Agreement.
                 -------

2.   Purchase, Sale, Transfer of Control, and Grant of Security Interest.
Subject to and on the terms provided in this Agreement, Torres sells the 3%Stock
for approximately $5,500 US Dollars ($51,786 Pesos 00/100 Currency of the United
Mexican States) (the "3%Stock Purchase Price") and the Partners purchase the
3%Stock, Torres agrees to transfer control of the 48%Stock to the Partners in
the manner described in paragraph F of the Recitals and the Partners agree to
take control of the 48%Stock in the manner provided in paragraph F of the
Recitals, or to transfer and take control in the alternative manner that the
parties may agree on pursuant to Section 2(e) of this Agreement, and Torres
agrees to perform consulting services for ATSI. Torres hereby grants a security
interest in the Telemarketing Stock to secure his obligation to transfer control
of the 48%Stock the Partners as provided in this Agreement. ATSI and the
Partners agree to deliver to Torres or his designees the First ATSI Shares, the
Second ATSI Shares, the Note and the Warrant in payment for sale of the 3%Stock,
transfer of control of the 48%Stock, performance of consulting services and
grant of a security interest.

                                       3
<PAGE>

     (a)  Upon Execution of this Agreement.  Contemporaneously with the
execution of this Agreement and as a condition to the effectiveness of this
Agreement,

     (1)  ATSI will:

          (A)  deliver to the Escrow Agent:

               (i)    400,000 shares of ATSI common stock in denominations of
                      50,000 (the "First ATSI Shares") and 350,000 (the "Second
                      ATSI Shares"),

               (ii)   a Note payable to the Torres Designee for $500,000 U.S.
                      Dollars, bearing interest at 6.62375% (the One Month
                      London Interbank Offer Rate published in the Wall Street
                      Journal on the day preceding the effective date of this
                      Agreement, maturing on demand five (5) days following the
                      Second Release or Simultaneous Release, as applicable, and
                      in the form attached as Exhibit 2(a)(1)(A)(ii) to this
                      Agreement (the "Note"); and

               (iii)  a Warrant for the purchase of 100,000 shares of ATSI
                      common stock having an exercise price of $6.00 and a term
                      of three years in the form attached as Exhibit
                      2(a)(1)(A)(iii) to this Agreement (the "Warrant");

          (B)  deliver to Torres:

               (i)    the Officer's Certificate in the form attached as Exhibit
                      2(a)(1)(B)-1;

               (ii)   the Secretary's Certificate in the form attached as
                      Exhibit 2(a)(1)(B)-2; and

               (iii)  the 3%Stock Purchase Price.
and

     (2)  Torres, Grupo and Telemarketing will:

          (A)  deliver to the Escrow Agent:

               (i)    the stock certificates for the Grupo Stock, endorsed in
                      blank;

               (ii)   the stock certificate for the RTorres Stock, endorsed in
                      blank; and

                                       4
<PAGE>

               (iii)  a document evidencing Torres agreement to refrain from
                      exercising his preemptive right to subscribe and pay
                      additional capital increases in Telemarketing in the form
                      attached as Exhibit 2(a)(2)(A)(iii) (the "Telemarketing
                      Waiver");

               (iv)   the Telemarketing Stock;

               (v)    an assignment of rights to the Telemarketing Stock to the
                      Partners in the form attached as Exhibit 2(a)(2)(A)(v)
                                                       ---------------------
                      (the "Telemarketing Stock Assignment"); and
                      -------------------------------------------

               (vi)   a Poder General naming the Partners in the form attached
                      as Exhibit 2(a)(2)(A)(vi) (the "Poder General");
                                                                     -

          (B)  deliver to ATSI:

          (i)  a Secretary Certificate for each of Grupo and Telemarketing in
               the form attached as Exhibit 2(a)(2)(B), and
                                    -----------------------

          (ii) a certified copy of the Minutes of Telemarketing's General
               Extraordinary Shareholder's Meeting held on February 10, 2000
               (the "Minutes"),
                              -

          (C)  deliver to the Partners a Poder Especial in the form attached as
               Exhibit 2(a)(2)(C) to this Agreement (the "Poder Especial").

     (b)  First Release. Upon SCT approval of the application filed by Grupo on
May 8, 2000 for the transfer of 49% of the Stock of Grupo from COMSAT Mexico to
ATSI pursuant to the COMSAT Agreement the "COMSAT SCT Approval"), ATSI may elect
to cause the Partners to take title to the 3%Stock by giving written notice to
Torres. If ATSI elects to cause the Partners to take title to the 3%Stock under
this paragraph, Torres and ATSI will each provide the other with an officer's
certificate in the form attached as Exhibit 2(b) to this Agreement updating
                                    ------------
their respective representations and warranties described in Sections 3 and 4
below, or stating any exceptions, within two Business Days of ATSI's notice of
its election to cause the Partners to take title to the 3%Stock. Provided there
has been no material change in the matters covered by the parties' respective
representations and warranties, on the first Business Day following receipt of
the officer's certificates (the "First Release Date") ATSI will pay to the
Torres Designee $100,000 U.S. Dollars in immediately available funds by wire
transfer to the account specified by Torres or the Torres Designee (which will
reduce the Note balance by $100,000), and each of Torres and ATSI will execute
and transmit to the Escrow Agent the First Release of Escrow in the form
attached as Exhibit A to the Escrow Agreement (providing for release to the
Torres Designee of the First ATSI Shares and release to the Partners of the
certificate for the 3% Stock (the "First Release").

                                       5
<PAGE>

Upon receipt of the certificate for the 3% Stock, the Partners will complete the
endorsement to themselves.

     (c)  Second Release. Within two (2) Business Days following satisfaction
of or ATSI's waiver of all of ATSI's conditions precedent described in Section 6
below, Torres and ATSI will provide the other with a certificate in the form
attached as Exhibit 2(b) to this Agreement updating their respective
representations and warranties described in Sections 3 and 4 below, or stating
any exceptions. Provided there has been no material change in the matters
covered by the parties' respective representations and warranties, on the first
Business Day following receipt of the officer's certificates (the "Second
Release Date") each of Torres and ATSI will execute and transmit to the Escrow
Agent the Second Release of Escrow in the form attached as Exhibit B to the
Escrow Agreement (providing for the release to the Torres Designee of the Second
ATSI Shares, the Warrant, the Note, the release to ATSI of the RTorresStock, and
the Telemarketing Waiver, the release to Torres of the 48%Stock and the
Telemarketing Stock, and if ATSI had not previously elected to complete the
First Release defined in Section 2(b) above, the release to the Torres Designee
of the First ATSI Shares and the release to ATSI of the 3%Stock) (the "Second
Release").

     (d)  Simultaneous Release. If the First SCT Release is obtained on or
before the COMSAT SCT Approval, within two (2) Business Days following the
satisfaction of or ATSI's waiver of all of ATSI's conditions precedent described
in Section 6 below (except for the COMSAT Closing described in Section 6(a)),
Torres and ATSI will provide the other with a certificate in the form attached
as Exhibit 2(b) to this Agreement updating their respective representations and
warranties described in Sections 3 and 4 below, or stating any exceptions.
Provided there has been no material change in the matters covered by the
parties' respective representations and warranties, on the first Business Day
following receipt of the officer's certificates (the "Simultaneous Release
Date") each of Torres and ATSI will execute and transmit to the Escrow Agent the
Simultaneous Release of Escrow in the form attached as Exhibit C to the Escrow
Agreement (providing for the release to the Torres Designee of the First ATSI
Shares, the Second ATSI Shares, the Warrant, and the Note, the release to Torres
the 48%Stock and the Telemarketing Stock, and the release to ATSI of the
3%Stock, the RTorresStock, and the Telemarketing Waiver (the "Simultaneous
Release"). Upon receipt of the certificate for 3%Stock, the Partners will
complete the endorsement to themselves.

     (e)  Alternative Structure. If the First SCT Approval, as defined in
Section 5(a) below, is denied, Torres and ATSI agree that the Escrow Agent will
release the Poder General to ATSI, that ATSI and Torres will cooperate to
perform the notarial process required to made the Poder General fully effective,
and that Torres and ATSI will work together to achieve the Partners' control of
the 48%Stock by an alternative means, including a direct transfer from Torres to
the Partners and any requisite approval from COFETEL and SCT for a direct
transfer. (The parties acknowledge that the First SCT Approval is deemed
approved if not denied by August 25, 2000).

                                       6
<PAGE>

     (f)  Termination of Escrow. If the Conditions Precedent defined in Section
(6) have not been satisfied by August 31, 2000, or if a certificate delivered by
Torres pursuant to subparagraphs 2 (b), (c), or (d) above reflects a material
adverse change in the representations and warranties of Grupo, Telemarketing or
Torres, then ATSI may terminate this Agreement by written notice of termination,
and may terminate the Escrow Agreement by delivering to the Escrow Agent the
Escrow Termination Notice in the form attached as Exhibit D to the Escrow
                                                  ---------

Agreement. If a certificate delivered by ATSI pursuant to subparagraphs 2 (b),
(c), or (d) above reflects a material adverse change in the representations and
warranties of ATSI, then Torres may terminate this Agreement by written notice
of termination, and may terminate the Escrow Agreement by delivering to the
Escrow Agent the Escrow Termination Notice in the form attached as Exhibit D to
                                                                   ---------
the Escrow Agreement.

     (g)  The parties acknowledge that ATSI's delivery of irrevocable
instructions to its transfer agent to deliver the stock certificate for the ATSI
Shares to the Escrow Agent constitutes delivery of the ATSI Shares;

     (h)  The parties acknowledge that the $100,000 U.S. Dollars cash described
in Section 2(b) includes payment of the $6,322.92 U.S. Dollar receivable from
Grupo to Torres;

     (i)  If ATSI defaults in its obligations under the Note, ATSI will pay as a
penalty fee to Torres One Hundred Thousand U.S. Dollars ($100,000) in addition
to the amounts due under the terms of the Note.

3.   Representations and Warranties of Torres. Torres represents and warrants
the following:

     (a)  Ownership of Stock. Torres owns good and marketable title to the
entire interest in the 3%Stock, the 48%Stock, and the Telemarketing Stock, and
is the record owner of the 3%Stock, the 48%Stock, and the Telemarketing Stock.
RTorres owns good and marketable title to entire interest in the RTorres Stock,
and is the record owner of the RTorres Stock. The 3%Stock, RTorres Stock and the
Telemarketing Stock are now and when delivered to the Partners will be free and
clear of all adverse claims, security interests, encumbrances, equities,
proxies, options, shareholder agreements or other restrictions and the 48%Stock
is delivered to Telemarketing free and clear of all adverse claims, security
interests, encumbrances, equities, proxies, options, shareholder agreements or
other restrictions.

     (b)  Organization and Good Standing; Qualification. Grupo and Telemarketing
are corporations duly organized, validly existing and in good standing under the
laws of Mexico, with all requisite corporate power and authority to carry on the
business in which engaged, to own their respective properties, to execute and
deliver this Agreement and to consummate the transactions contemplated by this
Agreement. Grupo and Telemarketing are duly qualified and licensed to do
business and are in good

                                       7
<PAGE>

standing in all jurisdictions where the nature of their business makes such
qualification necessary.

     (c)  Capitalization. The capital stock of Grupo consists of 543,513
shares of common stock, par value $1 Mexican Pesos per share, of which 543,513
shares are issued and outstanding. The capital stock of Telemarketing consists
of 1,000 shares of common stock, par value $1 Mexican Pesos per share, of which
1,000 shares are issued and outstanding. All of the issued and outstanding
shares of capital stock of Grupo and Telemarketing are duly authorized, validly
issued, fully paid and nonassessable. There are no options, warrants,
subscriptions or other rights to purchase, or securities convertible into or
exchangeable for, the capital stock of Grupo or Telemarketing. Neither Torres,
RTorres, Grupo nor Telemarketing are parties to or bound by, nor do any of them
have any knowledge of, any agreement, instrument, arrangement, contract,
obligation, commitment or understanding of any character, whether written or
oral, express or implied, relating to the sale, assignment, encumbrance,
conveyance, transfer or delivery of any capital stock of Grupo or Telemarketing.
No shares of capital stock of Grupo or Telemarketing have been issued or
disposed of in violation of the preemptive rights of any shareholder of Grupo or
Telemarketing.

     (d)  Corporate Records. The copies of the Certificate or Articles of
Incorporation and all amendments thereto and the Bylaws of Grupo and
Telemarketing that have been delivered to ATSI are true, correct and complete
copies as of the date of this Agreement. The minute books of Grupo and
Telemarketing, copies of which have been delivered to ATSI, contain accurate
minutes of all meetings of, and accurate consents to all actions taken without
meetings by the shareholders of Grupo and Telemarketing since the formation of
Grupo and Telemarketing, respectively.

     (e)  Authorization and Validity. The execution, delivery and performance
by Grupo and Telemarketing of this Agreement and the other agreements
contemplated hereby, and the consummation of the transactions contemplated
hereby and thereby, have been duly authorized by Grupo, Torres, and
Telemarketing. This Agreement and each other agreement contemplated hereby have
been duly executed and delivered by Grupo, Torres and Telemarketing and
constitute legal, valid and binding obligations of each of them, enforceable
against them in accordance with their respective terms, except as may be limited
by applicable bankruptcy, insolvency or similar laws affecting creditors' rights
generally or the availability of equitable remedies. The sale of the 3%Stock by
Torres to the Partners, the transfer of the RTorres Stock, and the transfer of
the 48%Stock by Torres to Telemarketing will not impair the ability or authority
of Grupo or Telemarketing to carry on their business as now conducted in any
respect.

     (f)  No Violation. Neither the execution, delivery or performance of this
Agreement or the other agreements contemplated hereby nor the consummation of
the transactions contemplated hereby or thereby will (i) conflict with, or
result in a violation or breach of the terms, conditions or provisions of, or
constitute a default under, the Certificate of Incorporation or Bylaws of Grupo
or Telemarketing or any agreement, indenture or other instrument under which
Grupo or Telemarketing is bound or to which

                                       8
<PAGE>

the 3%Stock, the 48%Stock, the Telemarketing Stock, the RTorres Stock, any of
the assets of Telemarketing or any of the assets of Grupo are subject, or result
in the creation or imposition of any security interest, lien, charge or
encumbrance upon the stock or any of the assets of Grupo or Telemarketing, or
(ii) violate or conflict with any judgment, decree, order, statute, rule or
regulation of any court or any public, governmental or regulatory agency or body
having jurisdiction over Grupo or Telemarketing, the 3%Stock, 48%Stock,
Telemarketing Stock, the RTorres Stock, or the assets of Grupo or Telemarketing.
Grupo and Telemarketing have complied with all laws, regulations and licensing
requirements and has filed with the proper authorities all necessary statements
and reports.

     (g)  Consents. Grupo, Telemarketing and Torres have obtained all consents,
authorizations, approvals, permits or licenses of, or have filed with, any
governmental or public body or authority, any lender or lessor, or any other
person or entity who is required to authorize, or whose authorization is
required in connection with, the execution, delivery and performance of this
Agreement or the agreements contemplated hereby on the part of Grupo,
Telemarketing or Torres, except for the approvals specifically contemplated by
Sections 5(b) and (c) of this Agreement.

     (h)  Assets. The balance sheet of Grupo attached as Exhibit 3(h)-1 and
Telemarketing attached as 3(h)-2 of this Agreement is true and complete and
fairly reflects the assets and liabilities of Grupo and Telemarketing,
respectively as of the date shown.

     (i)  Liabilities.  Except as described on the attached Exhibit 3(h), and
for the amounts that may arise from the costs of the interconnection projects
which might be recovered by Telefonos de Mexico, S.A. de C.V. and Telefonos del
Noroeste, S.A. de C.V. in terms of Cofetel's Resolution dated May 28, 1997,
neither Grupo nor Telemarketing has any liabilities, either accrued, contingent
or otherwise (known or unknown and asserted or unasserted), and neither Torres,
Telemarketing nor Grupo know of any basis for the assertion of any claims or
liabilities.

     (j)  No Material Change. There has been no material change in the condition
of Grupo or Telemarketing since the date of the balance sheets attached as
Exhibit 3(h), financial or otherwise, that has not been disclosed to ATSI's
senior management.

     (k)  Litigation. There are no legal actions or administrative proceedings
or investigations instituted, or to the best knowledge of Grupo, Telemarketing
or Torres threatened, against or affecting, or that could affect, Grupo or
Telemarketing, or any of the stock or the business of Grupo or Telemarketing.
Neither Grupo, Telemarketing nor Torres are (i) subject to any continuing court
or administrative order, writ, injunction or decree applicable specifically to
Grupo or Telemarketing or to either of their business, assets, operations or
employees or (ii) in default with respect to any such order, writ, injunction or
decree. Neither Grupo, Telemarketing nor Torres know of any basis for any such
action, proceeding or investigation.

                                       9
<PAGE>

     (l)  Operations. Currently Grupo is not conducting any operations other
than the preservation of the Long Distance Concession. The former operations of
Grupo are described on the attached Exhibit 3.l. Telemarketing has never had any
operations.

     (m)  Employees.  Currently Grupo does not have any employees. Telemarketing
does not have and has never had any employees.

     (n)  Agreements.  Besides the Surety Bonds executed with Afianzadora
Mexicana, S.A. and Fianzas Monterrey Aetna, S.A., and the Adhesion Contract to
the Trust Agreement executed with Banco Inverlat, S.A., Grupo is not a party to
any agreement with Torres or any third party, written or otherwise.
Telemarketing is not a party to any agreement with Torres or any third party,
written or otherwise.

     (o)  Officers. The individuals serving as officers of Grupo and
Telemarketing since their formation and their respective terms of service are
shown on Exhibit 3.o.
         -----------

     (p)  Agents. Neither Grupo nor Telemarketing has granted a power of
attorney to act on its behalf to any person or authorized any person to act as
an agent of Grupo or Telemarketing except for the officers listed on Exhibit
                                                                     -------
3.p.
---

     (q)  Laws. Grupo and Telemarketing are in compliance with and have complied
with all laws and regulations and have filed with the proper authorities all
necessary statements and reports.

     (r)  Long Distance Concession. Except as described on Exhibit 3.r., Grupo
                                                           ------------
has complied with the terms of the Long Distance Concession.

     (s)  Finders Fee.  Neither Grupo, Telemarketing nor Torres have incurred
any obligation for any finder's, broker's or agent's fee in connection with the
transactions contemplated hereby.

     (t)  Accuracy of Information Furnished. All information furnished to ATSI
by Grupo, Telemarketing or Torres in connection with the transactions
contemplated by this Agreement is true, correct and complete in all respects.
Such information states all facts required to be stated therein or necessary to
make the statements therein, in light of the circumstances under which such
statements are made, true, correct and complete. There is no material
information regarding Grupo, Telemarketing, the 4%Stock, the 47% Stock, the
Telemarketing Stock that has not been provided to ATSI.

     (u)  Competition. Neither Torres nor his Affiliates will provide intra-
Mexico long distance services to third parties or to seek to acquire a long
distance concession from the Mexican government, either directly or through the
acquisition of another entity, for a period of three (3) years from the date of
this Agreement. For the purposes of this subsection, "Affiliate" means any
person who controls, is controlled by, or is under common control with the
person referred to.

                                       10
<PAGE>

     (v)  Certain Payments. To the best knowledge of Grupo, Telemarketing and
Torres, respectively, neither Grupo nor Torres, nor any of their respective
directors, officers or employees has paid or caused to be paid, directly or
indirectly, in connection with the business of Grupo or Telemarketing:

     (i)   to any government or agency thereof or any agent of any supplier or
     customer any bribe, kick-back or other similar payment; or

     (ii)  any contribution to any political party or candidate (other than from
     personal funds of directors, officers or employees not reimbursed by their
     respective employers or as otherwise permitted by applicable law).

     (w)   Exemption from Securities Act. Torres understands that the ATSI
Shares are being transferred by ATSI in reliance on an exemption from the
registration requirements of the Securities Act of 1933, as amended (the
"Securities Act"), and equivalent state securities and "blue sky" laws, and that
ATSI is relying upon the accuracy of, and Torres' compliance with, the following
representations, warranties and covenants to determine the availability of these
exemptions:

     (i)   The person or persons who receive the ATSI Shares by indication of
     Torres will receive them for their own account, for investment purposes
     only and not with a view towards or in connection with the public sale or
     distribution thereof in violation of the Securities Act;

     (ii)  The person or persons referred to in paragraph (i) above are capable,
     by reason of their business and financial experience, of evaluating the
     relative merits and risks of an investment in the ATSI Shares, and are able
     to afford the loss of their investment in the ATSI Shares;

     (iii) The person or persons referred to in paragraph (i) above acknowledge
     that in making their decision to receive the ATSI Shares they have been
     given an opportunity to ask questions of and to receive answers from ATSI's
     executive officers, directors and management personnel concerning ATSI and
     the ATSI Shares;

     (iv)  The person or persons referred to in paragraph (i) above understand
     that the ATSI Shares have not been approved or disapproved by the United
     States Securities and Exchange Commission or any state securities
     commission and that the foregoing authorities have not reviewed any
     documents or instruments in connection with the transfer to them of the
     ATSI Shares and have not confirmed or determined the adequacy or accuracy
     of any such documents or instruments.

                                       11
<PAGE>

4.   Representations and Warranties of ATSI. ATSI represents and warrants the
following:

     (a)  Organization and Good Standing. ATSI is a corporation duly organized,
validly existing and in good standing under the laws of the state of its
incorporation, with all requisite corporate power and authority to carry on the
business in which it is engaged, to own the properties it owns, to execute and
deliver this Agreement and to consummate the transactions contemplated hereby.

     (b)  Capitalization. The authorized capital stock of ATSI consists of
100,000,000 shares of common stock, par value $.001 per share, of which
66,462,634 shares are issued and outstanding. All of the issued and outstanding
shares of capital stock of ATSI are duly authorized, validly issued, fully paid
and nonassessable. There are no options, warrants, subscriptions or other rights
to purchase, or securities convertible into or exchangeable for, the capital
stock of ATSI, other than as described on the attached Exhibit 4(b). ATSI is not
                                                       ------------
party to or bound by, nor it has any knowledge of, any agreement, instrument,
arrangement, contract, obligation, commitment or understanding of any character,
whether written or oral, express or implied, relating to the sale, assignment,
encumbrance, conveyance transfer or delivery of any capital stock of ATSI other
than as described on Exhibit 4(b). No shares of capital stock of ATSI have been
                     ------------
issued or disposed of in violation of the preemptive rights of any shareholder
of ATSI.

     (c)  Authorization and Validity. The execution, delivery and performance by
ATSI of this Agreement and the other agreements contemplated hereby, and the
consummation of the transactions contemplated hereby and thereby, have been duly
authorized by ATSI. This Agreement and each other agreement contemplated hereby
have been duly executed and delivered by ATSI and constitute legal, valid and
binding obligations of ATSI, enforceable against ATSI in accordance with their
respective terms, except as may be limited by applicable bankruptcy, insolvency
or similar laws affecting creditors' rights generally or the availability of
equitable remedies.

     (d)  No Violation. Neither the execution, delivery or performance of this
Agreement or the other agreements contemplated hereby nor the consummation of
the transactions contemplated hereby or thereby will (i) conflict with, or
result in a violation or breach of the terms, conditions and provisions of, or
constitute a default under, the Certificate of Incorporation or Bylaws of ATSI
or any agreement, indenture or other instrument under which ATSI is bound or
(ii) violate or conflict with any judgment, decree, order, statute, rule or
regulation of any court or any public, governmental or regulatory agency or body
having jurisdiction over ATSI or the properties or assets of ATSI.

     (e)  Finder's Fee. ATSI has not incurred any obligation for any finder's,
broker's or agent's fee in connection with the transactions contemplated hereby.

                                       12
<PAGE>

     (f)  Long Distance Concession. ATSI has reviewed the Long Distance
Concession, the Technical and Financial plans therein, and the extension granted
on April 11, 2000 to the starting of operations and obligations related, and
acknowledges the obligations and consequences deriving from the same.

     (g)  Accuracy of Information Furnished. All information furnished to Grupo,
Telemarketing or Torres by ATSI in connection with the transactions contemplated
by this Agreement, when read together with ATSI's public filings with the SEC is
true, correct and complete in all respects. Such information states all facts
required to be stated therein or necessary to make the statements therein, in
light of the circumstances under which such statements are made, true, correct
and complete. There is no information of an adverse nature regarding ATSI and
the ATSI Stock that has not been provided to Torres.

5.   Covenants.  The parties covenant as follows:

     (a)  Torres will work diligently to obtain the COMSAT SCT Approval and
approval from the SCT for the application filed May 24, 2000 for the approval of
the transfer of the 48%Stock to Telemarketing (the "First SCT Approval");

     (b)  Unless a Second Release or Simultaneous Release shall have occurred,
within three Business Days of receipt of the First SCT approval described in
Section 5(a) above, Torres will cause Grupo to take the appropriate corporate
steps to issue non-voting shares for 80% of its capital, and will file the
appropriate notices or applications for the issuance of the non-voting shares
with each of the SCT, SECOFI and other appropriate agencies of the Mexican
government, and work diligently to obtain those approvals (the "N Share
Approvals"). If a Second Release or Simultaneous Release shall have occurred,
Torres will assist ATSI as a consultant in preparing and filing the appropriate
notices or applications for the issuance of the non-voting shares and work
diligently with ATSI to obtain the N Share Approvals;

     (c)  Within three (3) Business Days of execution of this Agreement, ATSI
will provide Torres with a new name for Grupo (and several alternative names in
the event the name selected by ATSI if found not to be available by the SRE).
Within two (2) Business Days of receipt from ATSI of the name and alternative
names, Torres will cause Grupo to take the appropriate corporate steps to change
the name of Grupo to the name (or alternative name) selected by ATSI and file
the appropriate notice of application with the SRE regarding the change of the
name and work diligently to obtain approval from the SRE (the "SRE Approval").
Within 3 Business Days following the later to occur of the receipt of the SRE
Approval and the First SCT Approval, and provided a Second Release or
Simultaneous Release shall not have occurred, Torres will cause Grupo to file
the appropriate application with the SCT to approve the change of the name (the
"Second SCT Approval") and will work diligently to obtain approval from the SCT
for the change of the name; If a Second Release or Simultaneous Release shall
have occurred, Torres will assist ATSI as a consultant in preparing and filing
the appropriate notices or

                                       13
<PAGE>

applications for the change of the name of Grupo, and work diligently with ATSI
to obtain those approvals.

     (d)  Further Actions. The parties shall deliver any further instruments of
transfer and take all reasonable action as may be necessary or appropriate to
(i) vest in the Partner good and marketable title to the 3%Stock; (ii) vest in
the Partner good and marketable title to the RTorresStock, (iii) vest in
Telemarketing good and marketable title to the 48%Stock, (iv) carry out more
effectively the provisions of this Agreement, and (v) establish and protect the
rights created in favor of the parties; including, but not limited to, seeking
approval from the SCT, SRE, COFETEL, and other agencies of the government of
Mexico, and third parties, and completing any notarial process that may be
required under Mexican law. Upon a parties' reasonable request, the other
parties will provide additional information relevant to the transactions that
are the subject of this Agreement

     (e)  ATSI will assist Torres in obtaining the First SCT Approval, the SRE
Approval, the N Share Approvals, the Second SCT Approval, an additional
extension of the time to begin operations under the Long Distance Concession
from COFETEL, if needed, and any other governmental approvals required to
consummate the transactions describe in this Agreement to the extent reasonably
necessary and as requested by Torres.

     (f)  Notification of Breach of Representations and Warranties. Each party
will notify the others if it becomes aware that any of its representations and
warranties made in this Agreement were not true when made.

     (g)  Obligation to Hold ATSI Shares. The Torres Designee who receives the
First ATSI Shares and Second ATSI Shares will not transfer the ATSI Shares or
any rights with respect to the ATSI Shares for one year from the First Release
Date or Simultaneous Release Date, as applicable, and the Second Release Date or
Simultaneous Release Date as applicable, respectively. Following the expiration
of the one-year period, the Torres Designees may not sell the ATSI Shares except
pursuant to an exemption from United States registration requirements,
including, without limitation, Rule 144 under the Securities Act. Torres
acknowledges that ATSI has no obligation to register the ATSI Shares.

     (h)  ATSI Obligation to Repurchase ATSI Shares. At the option of the Torres
Designee to whom delivery of First ATSI Shares was made, to be exercised no
later than thirty (30) calendar days prior to the first anniversary of the First
Release Date or Simultaneous Release Date, as applicable, ATSI will buy back the
First ATSI Shares for $5.00 per share on the one year anniversary of the First
Release Date or Simultaneous Release Date, as applicable; and at the option of
the Torres Designee to whom delivery of the Second ATSI Shares was made, to be
exercised no later than thirty (30) days prior to the first anniversary of the
Second Release Date or Simultaneous Release Date, as applicable, ATSI will buy
back the Second ATSI Shares for $5.00 per share; provided however, ATSI shall
                                                 -------- -------
have no obligation to buy back more than an aggregate of 100,000 ATSI Shares
under this Section 5(h).

                                       14
<PAGE>

     (i)  ATSI's Obligation to Pay Additional Cash. If, on the first anniversary
of the First Release Date or Simultaneous Release Date, the closing sale price
of ATSI's common stock on The American Stock Exchange is less than $5.00 ATSI
will pay the Torres Designee cash equal to the difference between $5.00 and the
closing sale price on first anniversary of the First Release Date or
Simultaneous Date, as applicable, times the number of ATSI Shares that have not
been repurchased by ATSI pursuant to subparagraph 5(j) above; and if on the
                                     -----------------
first anniversary of the Second Release Date or Simultaneous Release Date, the
closing sale price of ATSI's common stock on The American Stock Exchange is less
than $5.00 ATSI will pay the Torres Designee cash equal to the difference
between $5.00 and the closing sale price on first anniversary of the Second
Release Date or Simultaneous Date, as applicable, times the number of ATSI
Shares that have not been repurchased by ATSI pursuant to subparagraph (h)
                                                          ----------------
above.

     (j)  Grupo and Telemarketing will take commercially reasonable steps to
maintain their condition as represented in Section 3 above, but except for
actions taken by the Partners pursuant to the Poder Especial or Poder General or
taken with the prior written consent of ATSI, neither Grupo nor Telemarketing
will acquire any assets, incur any liabilities, hire any employees, make any
regulatory filings, or make any other change in their condition, whether or not
material, without the prior consent of ATSI.

6.   ATSI's Conditions Precedent to Closing, As a condition precedent to the
Second Release of Escrow, the following conditions must be met or waived by
ATSI:

     (a)  COMSAT Closing.  There has occurred a "Release of Escrow" as defined
in the Agreement for Sale and Purchase Of Part of the Issued Share Capital of
Grupo Intelcom de Mexico, S.A de C.V. between COMSAT Mexico, S.A. de C.V. and
ATSI;

     (b)  Regulatory Approvals.  Torres has obtained the First SCT Approval;

     (c)  Name Change and Approval for Issuance of Non-Voting Shares. The
covenants described in Sections 5(b) and (c) above will have been performed and
completed;

     (d)  Tax Opinions or Escrow. Torres shall have delivered an opinion of a
CPA registered before the Taxpayer's Administration Services of Mexico, and
acceptable to ATSI, that

     (i)  ATSI is not obligated to withhold any part of the $500,000 or the ATSI
          Shares to satisfy any tax obligation of Torres, Grupo or Telemarketing
          arising from the consummation of the transactions described in this
          Agreement; and

     (ii) the closing of the transactions contemplated by this Agreement does
          not generate income tax to Grupo, Telemarketing, ATSI or the Partners,
          or if Torres is not able to deliver a satisfactory opinion, Torres has
          deposited

                                       15
<PAGE>

          into escrow with a mutually agreeable escrow agent under terms
          reasonably satisfactory to ATSI an amount sufficient to pay any income
          tax that may be assessed to ATSI.

     (e)  Corporate Records. Grupo and Telemarketing shall have delivered to
ATSI the original minute book of Grupo and Telemarketing and all other corporate
books and records.

7.   Indemnification.

     (a)  Indemnification by Torres. Torres agrees to indemnify, defend and hold
ATSI and each Partner, and each of their respective directors, officers, agents,
attorneys and affiliates harmless from and against all losses, claims,
obligations, demands, assessments, penalties, liabilities, costs, damages,
attorneys' fees and expenses arising under any theory of legal liability
(collectively, "Damages") asserted against or incurred by ATSI or the Partners
or any of their property by reason of or resulting from an actual or asserted
breach of this Agreement by Torres, Grupo or Telemarketing, including a breach
of any representation, warranty, or covenant of Torres in this Agreement or any
document delivered in connection with this Agreement.

     (b)  Indemnification by ATSI. ATSI agrees to indemnify defend and hold
Torres, the Torres Designee, and each of his attorneys and affiliates, harmless
from and against all Damages asserted against or incurred by them or any of
their property by reason of or resulting from an actual or asserted breach of
this Agreement by ATSI, including a breach of any of ATSI's representations,
warranties or covenants in this Agreement or any document delivered in
connection with this Agreement.

     (c)  Procedures. A person seeking indemnification under this Section shall
provide prompt notice of its claim for indemnification to the indemnifying
party, provided, however, that failure to give prompt notice shall not affect
the indemnifying party's obligations under this Section unless the failure
materially prejudices the indemnifying party's rights. The indemnified person
will have the right to select counsel to defend it in respect of any indemnified
matter under this Section, provided, however, that the counsel selected must be
reasonably satisfactory to the indemnifying party. The indemnified party will
keep the indemnifying party informed of the status of any litigation or dispute
resolution procedure, will give reasonable consideration to the suggestions and
requests of the indemnifying party with respect to the conduct of the litigation
or dispute resolution procedure, and will not settle any matter covered by this
Section without the prior consent of the indemnifying party, which shall not be
unreasonably withheld. Amounts due under this section shall be paid as incurred,
and may be offset against amounts due the indemnifying party under this
Agreement if not paid promptly.

8.   Release of Claims Against Grupo and Telemarketing. Torres hereby releases
Grupo and Telemarketing from any and all claims he may have against it arising
under

                                       16
<PAGE>

any theory of legal liability in any jurisdiction, including contingent and
unknown claims, and claims that accrue after the date of this Agreement.

9.   Miscellaneous.

     (a)  Amendment.  This Agreement may be amended, modified or supplemented
only by an instrument in writing executed by all the parties hereto.

     (b)  Assignment.  Neither this Agreement nor any right created hereby or in
any agreement entered into in connection with the transactions contemplated
hereby shall be assignable by any party hereto, except by ATSI to an affiliate
of ATSI.

     (c)  Survival.  The provisions of Sections 4, 5, 7 and 9 shall survive the
closing of the transactions contemplated by this Agreement (including the First
Escrow Release, Second Escrow Release, Simultaneous Escrow Release, Alternative
Escrow Release and Termination of Escrow) and shall continue indefinitely.

     (d)  Waiver.  No waiver by any party of any default or breach by another
party of any representation, warranty, covenant or condition contained in this
Agreement, any exhibit or any document, instrument or certificate contemplated
hereby shall be deemed to be a waiver of any subsequent default or breach by
such party of the same or any other representation, warranty, covenant or
condition. No act, delay, omission or course of dealing on the part of any party
in exercising any right, power or remedy under this Agreement or at law or in
equity shall operate as a waiver thereof or otherwise prejudice any of such
party's rights, powers and remedies. All remedies, whether at law or in equity,
shall be cumulative and the election of any one or more shall not constitute a
waiver of the right to pursue other available remedies.

     (e)  Parties In Interest; No Third Party Beneficiaries.  Except as
otherwise provided herein, the terms and conditions of this Agreement shall
inure to the benefit of and be binding upon the respective heirs, legal
representatives, successors and assigns of the parties hereto. Neither this
Agreement nor any other agreement contemplated hereby shall be deemed to confer
upon any person not a party hereto or thereto any rights or remedies hereunder
or thereunder, except for holders of ATSI Shares while such shares are
"restricted securities" or have benefits under the terms of Section 5.

     (f)  Entire Agreement.  This Agreement and the agreements contemplated
hereby constitute the entire agreement of the parties regarding the subject
matter hereof, and supersede all prior agreements and understandings, both
written and oral, among the parties, or any of them, with respect to the subject
matter hereof.

     (g)  Severability.  If any provision of this Agreement is held to be
illegal, invalid or unenforceable under present or future laws effective during
the term hereof, such provision shall be fully severable and this Agreement
shall be construed and enforced as if such illegal, invalid or unenforceable
provision never comprised a part hereof; and the remaining provisions hereof
shall remain in full force and effect and shall

                                       17
<PAGE>

not be affected by the illegal, invalid or unenforceable provision or by its
severance herefrom. Furthermore, in lieu of such illegal, invalid or
unenforceable provision, there shall be added automatically as part of this
Agreement a provision as similar in its terms to such illegal, invalid or
unenforceable provision as may be possible and be legal, valid and enforceable.

     (h)  Governing Law.  THIS AGREEMENT AND THE RIGHTS AND OBLIGATIONS OF THE
PARTIES HERETO SHALL BE GOVERNED BY AND CONSTRUED AND ENFORCED IN ACCORDANCE
WITH THE SUBSTANTIVE LAWS (BUT NOT THE RULES GOVERNING CONFLICTS OF LAWS) OF THE
STATE OF DELAWARE, U.S.A.; EXCEPT FOR MATTERS REGARDING THE CORPORATE GOVERNANCE
OF GRUPO OR COMSAT MEXICO, AND REQUIRED MEXICAN GOVERNMENTAL APPROVALS, WHICH
WILL BE GOVERNED BY MEXICAN LAW.

     (i)  Confidentiality. The parties agree that they will not disclose to any
third party (except to its agents or employees with a "need to know") any of the
other party's "Confidential Information," as defined below, or the fact that it
has possession of any of the other party's Confidential Information, whether the
Confidential Information was learned before or after the execution of the
Agreement, and whether it was transmitted in oral, paper, magnetic, photographic
or any other form. "Confidential Information" is any information regarding a
party's assets, liabilities, costs, rates, sales strategies, business plans,
suppliers, operations, financial results, identities of employees, identities of
customers, trade secrets, intellectual property, and any other information not
specifically listed that is commonly understood to be confidential. Provided,
however, that Confidential Information does not include any information which
enters the public domain legally and through no breach of this Agreement, or
other agreement, is independently developed by a party, is required to be
disclosed by applicable law (provided the disclosing party gives notice of the
disclosure at the earliest practical time) or is disclosed as part of a bona
fide legal proceeding brought by one party against the other in connection with
this Agreement. Each party will use the other's Confidential Information only in
connection with the performance of this Agreement, and will use at least a
reasonable degree of care to protect the Confidential Information. Each party
will return or destroy the other's Confidential Information on demand, and will
certify in writing, if requested, that the Confidential Information has been
destroyed.

     (j)  Captions.  The captions in this Agreement are for convenience of
reference only and shall not limit or otherwise affect any of the terms or
provisions hereof.

     (k)  Gender and Number.  When the context requires, the gender of all words
used herein shall include the masculine, feminine and neuter and the number of
all words shall include the singular and plural.

     (l)  Reference to Agreement.  Use of the words "herein", "hereof", "hereto"
and the like in this Agreement shall be construed as references to this
Agreement as a

                                       18
<PAGE>

whole and not to any particular Section or provision of this Agreement, unless
otherwise noted.

     (m)  Notice.  Any notice or communication hereunder or in any agreement
entered into in connection with the transactions contemplated hereby must be in
writing and given by depositing the same in the United States mail, addressed to
the party to be notified, postage prepaid and registered or certified with
return receipt requested, or by delivering the same in person or by facsimile
transmission. Such notice shall be deemed received on the date on which it is
hand-delivered or received by facsimile transmission or on the third Business
Day following the date on which it is so mailed. For purposes of notice, the
addresses of the parties shall be:

     If to ATSI:         American TeleSource International, Inc.
                         6000 Northwest Parkway, Suite 110
                         San Antonio, Texas 78249 U.S.A.
                         Attention: Arthur L. Smith
                         Telephone: (210) 547-1000
                         Facsimile: (210) 547-1001

     with a copy to:     Jackson Walker, L.L.P.
                         112 E. Pecan Street, Suite 2100
                         San Antonio, Texas 78205 U.S.A.
                         Attention: Patrick B. Tobin
                         Telephone: (210) 978-7700
                         Facsimile: (2100 978-7790

     If to Torres:       Alfonso Torres Roqueni
                         Blvd. M. Avila Camacho 184 16o. Piso,
                         Col. Lomas de San Isidro, C.P. 11620,
                         Mexico, D.F.
                         Telephone: (525) 281-1214
                         Facsimile: (525) 280-5860

Any party may change its address for notice by written notice given to the other
parties in accordance with this Section.

     (n) Choice of Forum. The parties hereto agree that should any suit, action
or proceeding arising out of this Agreement be instituted by any party hereto
(other than a suit, action or proceeding to enforce or realize upon any final
court judgment arising out of this Agreement), such suit, action or proceeding
shall be instituted only in a state or federal court in the State of Delaware,
U.S.A. Each of the parties hereto consents to the in personam jurisdiction of
                                                  -- --------
any state or federal court in the State of Delaware, U.S.A. and waives any
objection to the venue of any such suit, action or proceeding. The parties
hereto recognize that courts outside the State of Delaware, U.S.A. may also have
jurisdiction over suits, actions or proceedings arising out of this Agreement,
and in the event that any party hereto shall institute a proceeding involving
this Agreement in a

                                       19
<PAGE>

jurisdiction outside the State of Delaware, U.S.A., the party instituting such
proceeding shall indemnify any other party hereto for any losses and expenses
that may result from the breach of the foregoing covenant to institute such
proceeding only in a state or federal court in the State of Delaware, U.S.A.,
including without limitation any additional expenses incurred as a result of
litigating in another jurisdiction, such as reasonable fees and expenses of
local counsel and travel and lodging expenses for parties, witnesses, experts
and support personnel.

     (o)  Service of Process.  Service of any and all process that may be served
on any party hereto in any suit, action or proceeding arising out of this
Agreement may be made in the manner and to the address set forth in this Section
and service thus made shall be taken and held to be valid personal service upon
such party by any party hereto on whose behalf such service is made.

     (p)  Counterparts.  This Agreement may be executed in multiple
counterparts, each of which shall be deemed an original, and all of which
together shall constitute one and the same instrument.

                  REMAINDER OF PAGE INTENTIONALLY LEFT BLANK

                                       20
<PAGE>

     EXECUTED as of the date first above written.

                                        AMERICAN TELESOURCE
                                        INTERNATIONAL, INC.

                                        By:   _______________________________
                                        Name: _______________________________
                                        Its:  _______________________________
                                        Date: __________________

                                        _____________________________________
                                        Alfonso Torres Roqueni
                                        Date: __________________

                                        GRUPO INTELCOM DE MEXICO,
                                        S.A DE C.V.

                                        By:   _______________________________
                                        Name: _______________________________
                                        Its:  _______________________________
                                        Date: __________________

                                        TELEMARKETING DE MEXICO,
                                        S.A. DE C.V.

                                        By:   _______________________________
                                        Name: _______________________________
                                        Its:  _______________________________
                                        Date: __________________

                                       21
<PAGE>

Exhibits

1                 Escrow Agreement
2(a)(1)(A)(ii)    Note
2(a)(1)(A)(iii)   Warrant
2(a)(1)(B)-1      ATSI Officer Certificate
2(a)(1)(B)-2      ATSI Secretary Certificate
2(a)(2)(A)(iii)   Telemarketing Waiver
2(a)(2)(A)(v)     Telemarketing Stock Assignment
2(a)(2)(A)(vi)    Poder General
2(a)(2)(B)        Form of Grupo and Telemarketing Secretary Certificate
2(a)(2)(C)        Poder Especial
2(b)              Officers Certificate Updating Representations and Warranties
3(h)-1            Balance Sheet of Grupo
3(h)-2            Balance Sheet of Telemarketing
3(l)              Description of Operations of Grupo and Telemarketing
3(o)              Officers of Grupo and Telemarketing
3(p)              Agents of Grupo and Telemarketing
3()               Compliance with Long Distance Concession
4(b)              Capital Stock of ATSI

                                       22

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