Document:

<PAGE>

                                                                     EXHIBIT 4.2

                      THE CONCENTRIC NETWORK CORPORATION

                                  NETHERLANDS

                              SHARE OPTION SCHEME
<PAGE>

                               TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                            Page
                                                                            ----
<S>                                                                         <C>
1.   Purposes..............................................................    1
     --------
2.   Definitions and interpretation........................................    1
     ------------------------------
3.   Selection of Eligible Employees.......................................    3
     -------------------------------
4.   Grant of Options......................................................    3
     ----------------
5.   Exercise of an Option.................................................    4
     ---------------------
6.   Period of Option and provisions for Participants leaving the Group....    4
     ------------------------------------------------------------------
7.   Variation of capital..................................................    5
     --------------------
8.   Exchange of Options...................................................    6
     -------------------
9.   Takeover and liquidation..............................................    6
     ------------------------
10.  Rights attaching to shares allotted pursuant to an Option.............    7
     ---------------------------------------------------------
11.  Availability of shares................................................    7
     ----------------------
12.  General...............................................................    7
     -------
</TABLE>

                                      -i-
<PAGE>

                                                            DRAFT AS OF 02/04/00

      The Concentric Network Corporation Netherlands Share Option Scheme

1.   Purposes
     --------

     The purposes of the Concentric Network Corporation Netherlands Share Option
Scheme are (i) to attract and retain the best available personnel for positions
of substantial responsibility, (ii) to provide additional incentive to Eligible
Employees, and (iii) to promote the success of the Company's business. The
Scheme allows the Company to grant Options to purchase Ordinary Shares to
Eligible Employees to achieve these purposes.

2.   Definitions and interpretation
     --------------------------------

     2.1 For the purposes of the Scheme, unless the context otherwise requires,
the following words and expressions shall have the following meanings:

     "the Adoption Date"                means the date on which the Board passes
                                        a resolution adopting the Scheme;

     "the Auditors"                     means the auditors for the time being of
                                        the Company (acting as experts and not
                                        as arbitrators);

     "the Board"                        means the board of directors of the
                                        Company or the persons appointed by the
                                        board of directors of the Company to act
                                        as a committee for all or any matters
                                        relating to the Scheme;

     "the Company"                      means Concentric Network Corporation
                                        registered in Delaware;

     "Control"                          has the same meaning as in article 10a
                                        paragraph 5 of the US Taxes Act;

     "Date of Grant"                    means the date on which an Option is,
                                        was, or is to be granted under the
                                        Scheme;

     "Disability"                       means total and permanent disability, as
                                        evidenced to the satisfaction of the
                                        Board;

     "Eligible Employee"                means a person who is at the relevant
                                        Date of Grant a Full-Time Director or a
                                        Qualifying Employee in either case of a
                                        company selected by the Board to
                                        participate in the Scheme;
<PAGE>

     "Full-Time Director"               means a director of the Company and/or
                                        any Subsidiary whose terms of office or
                                        employment require him to work for at
                                        least twenty-five hours per week
                                        (excluding meal breaks);

     "Group"                            means the Company and the Subsidiaries;

     "Option"                           means an option to acquire Scheme Shares
                                        granted pursuant to the Scheme;

     "Option Price"                     in relation to any Scheme Share means an
                                        amount determined by the Board being
                                        equal to the amount determined to be the
                                        market value on the Date of Grant of an
                                        Ordinary Share;

     "Ordinary Shares"                  means shares of common stock of the
                                        Company;

     "Participant"                      means any person who for the time being
                                        participates in the Scheme;

     "Qualifying Employee"              means an employee of the Company and/or
                                        a Subsidiary (who is not a director of
                                        the Company or a Subsidiary);

     "Qualifying Employment"            means office or employment either as a
                                        Full-Time Director or as a Qualifying
                                        Employee as the case may be;

     "Record Date"                      in relation to any particular payment of
                                        dividend or the making of any other
                                        distribution to the Company's
                                        stockholders means the date on which any
                                        such stockholder must duly be recognised
                                        as such by the Company in order to have
                                        the right to receive such dividend or
                                        other distribution;

     "the Rules"                        means these rules as from time to time
                                        amended;

     "the Scheme"                       means The Concentric Network Corporation
                                        Netherlands Share Option Scheme
                                        constituted and governed by the Rules;

     "Scheme Shares"                    means Ordinary Shares to be acquired by
                                        a Participant on the exercise by him of
                                        an Option;

                                      -2-
<PAGE>

     "Subsidiary"                       means any body corporate of which the
                                        Company is for the time being to be
                                        taken to have Control and which is a
                                        subsidiary of the Company within article
                                        10a, paragraph 4 of the US Taxes Act;

     "Subsisting Option"                means an Option which has neither lapsed
                                        nor been exercised;

     2.2 Where the context so permits the singular shall include the plural and
vice versa and the masculine shall include the feminine.

     2.3 Reference to any Act shall include any statutory modification,
 amendment or re-enactment thereof.

3.   Selection of Eligible Employees
     -------------------------------

     3.1 The Board may from time to time at its discretion grant an Option to an
Eligible Employee to be selected in each case at the discretion of the Board
pursuant to the terms of the Scheme.

4.   Grant of Options
     ----------------

     4.1 Subject to the limitations referred to herein, the Board shall
determine the number of Scheme Shares to be included in an Option.

     4.2 Options may be exercised on the Date of Grant, subject to the
provisions of the Option Certificate.

     4.3 As soon as practicable after Options have been granted, the Board shall
issue to each Participant an Option Certificate in the form of a deed specifying
the option price and carrying a statement to the effect of Rule 4.4. The Option
Certificate may also contain other terms and conditions which are relevant to
the Option.

     4.4 An Option granted to an Eligible Employee shall not be transferable by
the Eligible Employee other than by will or the laws of descent and
distribution.

     4.5 The amount payable upon the exercise of an Option shall be the Option
Price.

     4.6 Subject to the provisions of Rule 7, the total number of Ordinary
Shares issued or remaining to be issued on the exercise of Options granted under
the Scheme shall not exceed [1,000,000] Ordinary Shares. For the avoidance of
doubt, shares subject to an Option which has lapsed, been cancelled or
surrendered shall not count towards the above limits.

                                      -3-
<PAGE>

     4.7  The granting of Options does not qualify as an employment condition
and is purely discretionary to the Board.

5.   Exercise of an Option
     ---------------------

     5.1  An Option shall be exercised by delivering to the Secretary of the
Company a notice duly signed by the Participant in a form approved by the Board
together with payment by cheque or in cash of the Option Price for each Scheme
Share to be acquired and delivery of the Option Certificate for amendment or
cancellation as the case may be. An Option may be exercised in part but may not
be exercised in respect of a fraction of a Scheme Share.

     5.2  Subject to any necessary consents and to an Option having been
exercised in accordance with the provisions of Rule 5.1, the Board shall as soon
as practicable make an allotment or procure the transfer to the Participant or
his nominee of the number of Scheme Shares specified in the notice exercising
the Option. Until the issuance (as evidenced by the appropriate entry on the
books of the Company or of a duly authorized transfer agent of the Company) of
the stock certificate evidencing such Shares, no right to vote or receive
dividends or any other rights as a shareholder shall exist with respect to the
Ordinary Shares, notwithstanding the exercise of the Option.

6.   Period of Option and provisions for Participants leaving the Group
     ------------------------------------------------------------------

     6.1  An Option may not be exercised later than the day specified in the
Option Certificate (the "Expiration Date"). An Option shall lapse on the
Expiration Date. The Expiration Date may not be later than the day before the
tenth anniversary of the date that the Option was granted.

     6.2  Except as provided in Rules 6.4, 6.5 and 6.6 any Option will lapse at
the moment the Participant is not longer in Qualifying Employment.

     6.3  Exercise of an Option shall only be effective provided that any income
or withholding tax liability arising to the Participant at the date of
exercising the Option is accompanied by payment of a sum equal to the tax due.

     6.4  Subject to Rule 6.1, if a Participant ceases to be in Qualifying
Employment by reason of Disability, the Participant may exercise an Option in
accordance with the provisions of the Option Certificate. The Participant may
only exercise such Option within the period of time specified in the Option
Certificate (the "Termination Period"). If the Termination Period is not
specified in the Option Certificate, the Participant may exercise such Option
within 12 months of the date of cessation of employment and shall thereafter
cease to have any rights to exercise that Option.

                                      -4-
<PAGE>

     6.5  Subject to Rule 6.1, if a Participant dies whilst in Qualifying
Employment, his personal representatives may within the Termination Period
(which shall not exceed 12 months from the date of death) exercise an Option in
accordance with the provisions of the Option Certificate. If the Termination
Period is not specified in the Option Certificate, his personal representatives
may exercise such Option within 12 months of the Participant's death and shall
thereafter cease to have any rights to exercise that Option.

     6.6  Subject to Rule 6.1, if a Participant ceases to be in Qualifying
Employment for any reason other than those specified in Rules 6.4 or 6.5, the
Participant may within the Termination Period exercise an Option in accordance
with the provisions of the Option Certificate. If the Termination Period is not
specified in the Option Certificate, the Participant may exercise such Option
within 3 months of the cessation of his employment and shall thereafter cease to
have any rights to exercise that Option.

     6.7  If a Participant (or his personal representatives) shall cease to have
any rights to exercise an Option under this Rule such Option shall lapse.

     6.8  Unless the Board provides otherwise, a Participant shall not be in
Qualifying Employment during any unpaid leave of absence.

7.   Variation of capital
     --------------------

     7.1  In the event of any variation in or reorganisation of the share
capital of the Company whether by way of capitalisation or offer by way of
rights or reduction, sub-division or consolidation of shares, or otherwise,
then:

          (A)  the Option Price in respect of any Options granted pursuant to
the Scheme; and/or

          (B)  the number of Scheme Shares subject to any such Option;

shall be varied by the Board in such manner as the Auditors advise to be in
their opinion fair and reasonable. Such variation by the Board shall be final
and binding on the Participants and the Company.

     7.2  In no circumstances shall the Option Price as reduced or adjusted
pursuant to Rule 7.1 in respect of any Scheme Share be less than the nominal
value of such share.

                                      -5-
<PAGE>

8.   Exchange of Options
     -------------------

     8.1  This Rule 8 applies where a company ("the Acquiring Company") obtains
Control of the Company as a result of:

          (A)  a general offer to acquire the whole of the issued share capital
of the Company (other than that which is already owned by it) made on a
condition such that if satisfied the Acquiring Company will have Control of the
Company; or

          (B)  a general offer to acquire all the Ordinary Shares (or such
Ordinary Shares as are not already owned by the Acquiring Company).

     8.2  If as a result of the events specified in Rule 8.1(A) and 8.1(B) the
Acquiring Company has obtained Control of the Company, the Company shall seek
the agreement of the Acquiring Company, and if such agreement is obtained, the
Company shall forthwith notify each Participant thereof and any Subsisting
Option shall be released by the Participant for a new Option on terms agreed
between the Company and the Acquiring Company and certified by the Auditors as
fair and reasonable.

     8.3  The provisions of this Rule 8 shall apply with any consequential
amendments in the event that Control of the Acquiring Company itself changes as
a result of the events specified in Rule 8.1.

9.   Takeover and liquidation
     ------------------------

     9.1  If the agreement of the Acquiring Company (as defined in Rule 8.1)
cannot be obtained for the release of Subsisting Options for new options in
accordance with Rule 8.2, then all Subsisting Options shall lapse immediately
prior to the consummation of a transaction described in Rule 8.1.

     9.2  If a notice of a meeting to consider a resolution for any other
voluntary winding up of the Company shall be given, the Board shall notify a
Participant 10 days prior to the commencement of the winding up that he shall be
entitled (subject to Rules 6.1 and 6.2) to exercise any Subsisting Option then
held by him. All Subsisting Options shall lapse on the winding up of the
Company.

     9.3  Upon the Board becoming aware that any of the events referred to above
has happened, the effect thereof shall be notified forthwith by the Board to the
Participants.

                                      -6-
<PAGE>

10.  Rights attaching to shares allotted pursuant to an Option
     ---------------------------------------------------------

     All Scheme Shares allotted pursuant to the exercise of any Option shall as
to voting, dividend, transfer and other rights including those arising in the
liquidation of the Company, rank equally in all respects and as to one class
with the Ordinary Shares of the Company in issue as at the date of such
allotment, save that any allotment made after the earlier of the date of
announcement of a proposed dividend or other distribution and the Record Date of
a proposed dividend or other distribution shall be made upon terms that the
Ordinary Shares so allotted are not entitled to participate therein.

11.  Availability of shares
     ----------------------

     The Company will at all times keep sufficient authorised but unissued
Ordinary Shares or have under its control sufficient issued Ordinary Shares to
permit the exercise of all unexercised Options.

12.  General
     -------

     12.1   Participation in the Scheme by a Participant is a matter entirely
separate from, and shall not affect, his pension rights and terms of employment
and, in particular (but without prejudice to the generality of the foregoing),
if a Participant shall cease for any reason (including, but without prejudice to
the generality of the foregoing, his wrongful dismissal) to be employed by or
hold office in the Company and/or any Subsidiary he shall not be entitled by way
of compensation for loss or otherwise howsoever, to any sum or benefit to
compensate him for the loss of any right or benefit under the Scheme.

     12.2   The Company shall maintain all necessary books of account and
records relating to the Scheme.

     12.3   The Scheme shall in all respects be administered by the Board which
may make such Rules not being inconsistent with the terms and conditions hereof
for the conduct of the Scheme as the Board thinks fit. Any dispute regarding the
interpretation of the Rules or the terms of any Option shall be determined by
the Board (upon such advice as it shall consider necessary) and its decision
shall be final and binding.

     12.4   A Participant who is a director of the Company may, notwithstanding
his interest, vote on any resolution of the Board or the board of directors of
the Company concerning the Scheme (other than in respect of his own
participation therein) and may retain any benefits under the Scheme.

                                      -7-
<PAGE>

     12.5   The Board or the Company in general meeting may at any time
terminate the Scheme and in such event no further Options will be granted but
the subsisting rights of Participants will not thereby be affected.

     12.6   The Board shall not grant Options and no Eligible Employee shall
exercise an Option or transfer any rights pursuant to an Option, while being in
the possession of inside information as set forth in US or Netherlands inside
trading legislation.

                                      -8-
<PAGE>

      The Concentric Network Corporation Netherlands Share Option Scheme

                            The option certificate

Article 1

This is to certify that ......................................... of
 ................................................ (hereinafter: the Employee) has
been granted an Option to acquire ordinary shares in Concentric Network
Corporation in accordance with and subject to the Rules of the Concentric
Network Corporation Netherlands Share Option Scheme.

Details of the Option are as follows:

<TABLE>
======================================================================================================
(1)                                 (2)                                 (3)
Number of shares over               Option Price per Share              Date of Grant of Option
which the Option is held
------------------------------------------------------------------------------------------------------
<S>                                 <C>                                 <C>
======================================================================================================
</TABLE>

Article 2
The Option is exercisable in accordance with the Rules of the said Scheme.

Article 3
The Option is personal and is not capable of assignment. Any purported
assignment, pledge, disposal of or dealing with an Option shall cause the Option
to lapse forthwith.

Article 4
The Expiration Date will be .......................... [10 years after the date
of grant].

Article 5
At the Date of Grant, the Option becomes immediately and fully exercisable.

Article 6
If and insofar the Employee exercises the Option, the Employee is obliged to
immediately sell the Scheme Shares acquired.

Article 7
If the Employee has sold the Scheme Shares as mentioned in article 6, the
Employee is obliged to provide the Company with copies of the documents
regarding this sell.

Article 8
In the event the Qualifying Employment ends before ......................... [4
years after the date of grant], other than due to death of the Employee, a
penalty shall be due by the Employee if and insofar as the Option is exercised
before termination date (the Reimbursement).
<PAGE>

Article 9
The Reimbursement is determined by the Benefit of the Option, based upon the
following:
 .    if the Option is exercised by the Employee before one year's anniversary:
     100% of the Benefit;
 .    if the Option is exercised by the Employee on one year's anniversary: 75%
     of the Benefit;
 .    thereafter, if the Option is exercised by the Employee after one year's
     anniversary, the percentage of 75 will decrease with 2.1 for each full
     month the Qualifying Employment exists after ................. [4 years
     after the date of grant].

Article 10
The Benefit will be determined at the difference between the fair market value
of the shares at the moment of exercise of the Option and the exercise-price of
the Option, minus taxes due upon exercise.

Article 11
Any tax and/or social security liabilities in connection with this Option will
be for the account of the Employee. By signing this Option Certificate, the
Employee declares to agree that the tax and/or social security liabilities are
exclusively levied at the moment the Option is exercised. The taxable value
amounts to the difference between the fair market value of the Scheme Shares and
the exercise price of the Option. The Employee will not take another position by
filing his individual income tax return.

Article 12
A form of exercise is printed on the reverse of this certificate.

THE COMMON SEAL of the Company was hereunto affixed in the presence of

_______________________________________
Director

_______________________________________
Director/Secretary

THIS CERTIFICATE SHOULD BE KEPT IN A SAFE PLACE. YOU WILL NEED TO PRODUCE IT IN
ORDER TO ACQUIRE THE SHARES SHOWN.
<PAGE>

                         NOTICE OF EXERCISE OF OPTION

I am entitled to exercise an Option under the Concentric Network Corporation
Netherlands Share Option Scheme as set out in the Option Certificate overleaf.

I now apply for shares indicated below and request that you arrange for the
allotment and immediately sell of these shares.

Number of shares applied for ______________
I enclose the sum of NLG ___________ in cash being payment in full for those
shares at the option price per share shown on the option certificate.

OR

I enclose a cheque made payable to [             ] for NLG _____________ being
payment in full for those shares at the option price per share shown on the
option certificate.

and confirm that as regards any tax liability arising upon exercise of the
Option, to the extent that the amount of such liability cannot be deducted in
full from my salary:

(a)  I agree (and the Company has consented) to repay such amount to the     [_]
     Company in instalments by way of deduction from salary; or
(b)  the cheque accompanying this notice of exercise includes a sum equal    [_]
     to the amount due.

Please tick the appropriate box and speak to [the Company Secretary] for
guidance if required.

Personal Details (block capitals)

Mr/Mrs/Miss/Ms__________________________________________________________________
FORENAMES_______________________________________________________________________
ADDRESS_________________________________________________________________________
 _______________________________________________________________________________
POSTCODE________________________________________________________________________
SIGNED__________________________________________________________________________
DATE____________________________________________________________________________
<PAGE>

                                                                        Addendum

Concentric Network Corporation Netherlands Share Option Scheme

Example

exercise price of the option                  NLG 100
fair market value of a share after 2 years    NLG 150

The employee leaves the company two years (24 months) after the option is
granted. The option is exercised before termination date. The employee is
obliged to immediately sell the shares acquired.

The taxable benefit at the moment of exercising the option amounts to NLG 150
minus NLG 100 = NLG 50. Assuming that the maximum tax rate of 60% applies, the
taxation amounts to NLG 30 (= NLG 50 x 60%). Based on article 10 of the option
certificate, the benefit amounts to NLG 50 minus NLG 30 = NLG 20.

Article 8 and 9 of the certificate determine that 49.8% (see the schedule
attached) of the benefit must be paid by the employee to the employer. The
benefit is determined in article 10. As a result, the penalty amounts to NLG
9.96 (=NLG 20 x 49.8%).

Benefit of the option                              NLG 50.00
Minus: taxation                                    NLG 30.00 -/-
Minus: penalty                                     NLG  9.96 -/-
                                                   ---------
Net result                                         NLG 10.04
                                                   =========<PAGE>

                                                                     Exhibit 4.1

                      Agreement for the Sale and Purchase
                    Of Part of the Issued Share Capital of
                    Grupo Intelcom de Mexico, S.A. de C.V.

     This Agreement (this "Agreement") dated effective as of June 6, 2000 is
between COMSAT Mexico, S.A. de C.V., a Mexican corporation with principal
offices located at Av. Renato Leduc 321 Col. Toriello Guerra, Tlalpan, C.P.
14050, Mexico ("COMSAT Mexico" or "Seller"), and American TeleSource
International, Inc., a Delaware corporation with principal offices at 12500
Network Boulevard, San Antonio, Texas, USA ("ATSI" or "Purchaser"). Seller and
Purchaser shall each be referred herein, individually, as a "Party" and,
collectively, as the "Parties".

                                   RECITALS

  A.  Grupo Intelcom de Mexico, S.A. de C.V. (the "Company") is a corporation
      organized under the laws of Mexico;

  B.  COMSAT Mexico owns Two Hundred Sixty Six Thousand, Two Hundred Thirty One
      (266,231) shares of the stock of the Company (which shares shall be
      referred to herein as the "Shares"), representing forty-nine percent (49%)
      of the issued and outstanding shares of Company stock;

  C.  COMSAT Mexico desires to sell the Shares to ATSI, and ATSI desires to
      purchase the Shares from COMSAT Mexico in accordance with the terms and
      conditions set forth in this Agreement.

  Therefore, for the consideration described in this Agreement and for other
consideration the receipt and sufficiency of which is hereby acknowledged, the
Parties agree as follows:

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

  "Closing" shall have the meaning given in Section 4 below.

  "CFCE" shall mean the Comision Federal de Competencia Economica de Mexico.

  "COFETEL" shall mean the Comision Federal de Telecomunicaciones de Mexico.

  "Escrow Termination Date" shall mean September 30, 2000, or any later date
  that may be established by COFETEL for the start of operations under the Long
  Distance License.

  "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
  duly 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

                                       1
<PAGE>

  after duly diligent investigation and in inquiry by the principal executive
  officer of that entity, or such officer's representative.

  "Escrow Agent" - Chase Bank of Texas, N.A. serving as escrow agent under
  the terms of the Escrow Agreement attached as Exhibit 1.
                                                ---------

  "Escrow Deposit" shall have the meaning given in Section 4(d) below.

  "Long Distance License" means that concession issued on June 4, 1998 by the
  SCT to the Company.

  "Majority Shareholder" shall mean Dr. Alfonso Roqueni Torres, an individual
  who, as of the date of this Agreement, owns fifty-one percent (51%) of the
  issued and outstanding shares of the Company.

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

  "SRE" shall mean Secretaria de Relaciones Exteriores de Mexico.

2.   Sale and Purchase of Shares. Subject to the terms of this Agreement, the
Seller sells, and the Purchaser purchases for the purchase price set forth in
Section 3 below, the Shares.

3.   Purchase Price. The purchase price for the Shares shall be Seven Hundred
and Fifty Thousand and no 00/100's U.S. Dollars ($750,000.00)(the "Purchase
Price").

4.   Closing. The parties agree that the following must occur contemporaneously
with the execution of this Agreement and as a condition to the effectiveness of
this Agreement (the "Closing"):

     (a)  Escrow Agent, Seller and Purchaser shall have executed the Escrow
Agreement attached as Exhibit 1 and each party shall have received evidence of
                      ---------
execution via facsimile, with original to follow via overnight mail to the
address provided for each party in Section 11 of this Agreement;

     (b)  Each party shall have received evidence of execution of this Agreement
by the other party via facsimile with original to follow via overnight mail to
the addresses provided for each party in Section 11 of this Agreement;

     (c)  Purchaser shall have delivered Six Hundred Seventy Five Thousand U.S.
 Dollars and no 00/100's ($675,000.00) to Seller in immediately available funds
 by wire transfer to the Seller's account at Citibank, NA ABA 021000089 Account
 Number 3617-7326 Account Name: COMSAT Mexico, S.A. de C.V.

     (d)  Purchaser shall have delivered Seventy Five Thousand U.S. Dollars and
no 00/100's ($75,000.00) to the Escrow Agent in immediately available funds by
wire

                                       2
<PAGE>

transfer to the Escrow Agent's account at: Chase Bank of Texas, N.A. - Houston,
TX, ABA #: 113000609, Credit: Trust Clearing Account #00101606276, FFC: American
TeleSource/COMSAT Escrow Account #21180-00, Attn: May Ng x6467 (the "Escrow
Deposit");

     (e)  Seller shall have delivered duly executed transfers of the Shares to
the Escrow Agent;

     (f)  Seller shall have delivered an Officer's Certificate in the form
attached as Exhibit 4(f)-1 executed by its Director General and a Secretary's
Certificate in the form attached as Exhibit 4(f)-2; and

     (g)  Purchaser shall have delivered an Officer's Certificate in the
form attached as Exhibit 4(g)-1 executed by its Chief Executive Officer and the
Secretary's Certificate in the form attached as Exhibit 4(g)-2 executed by its
Secretary.

5.   Release of Escrow. Seller and Purchaser, acting in good faith, shall
execute the Release of Escrow in the form attached as Exhibit A of the Escrow
Agreement no later than the third business day following the satisfaction of the
Conditions Precedent to Release of Escrow described in Section 6 below. In the
event that such conditions precedent are not satisfied by the Escrow Termination
Date, then this Agreement may be terminated by either Party by the provision of
written notice to the other Party and the Escrow Deposit and the Shares will be
returned in accordance with the Escrow Agreement.

6.   Conditions Precedent to Purchaser's Obligation to Release Escrow.
Purchaser's obligation to execute the Release of Escrow is subject to the
satisfaction of the following conditions precedent:

     (a)  Majority Shareholder Agreement. Purchaser and the Majority Shareholder
shall have executed an Agreement for the transfer of control of the Majority
Shareholder's interest in the Company and the required regulatory notices and
applications in connection with the transfer of the Majority Shareholder's
interest in the Company shall have been made;

     (b)  Resignations of Officers. All of the officers of the Company, if any,
shall have tendered their resignations (which resignations may be contingent
upon the completion of the Release of Escrow contemplated hereunder);

     (c)  Consents. The following consents and approvals have been obtained or
applied for, as indicated below:

          (i)   SCT approval required for the transfer of the Shares to
                Purchaser shall have been obtained;

                                       3
<PAGE>

          (ii)  SRE approval required for change of the name of the Company to a
                name mutually agreeable to the parties (which shall not include
                the word "COMSAT") shall have been obtained, and application to
                the SCT for the change of the name shall have been made.

          (iii) CFCE approval, if required, for transfer of the shares to
                Purchaser shall have been obtained.

7.   Representations and Warranties of Seller. Seller represents and warrants
the following as of the date of this Agreement:

     (a)  Ownership of Stock. Seller owns good and marketable title to the
entire interest in the Shares, is the record owner of the Shares, and the Shares
are delivered to Purchaser free and clear of all adverse claims, security
interests, encumbrances, proxies, options, shareholder agreements or other
restrictions (except those which may be imposed under Mexican or U.S. law or
regulation).

     (b)  Organization and Good Standing; Qualification. Seller is a sociedad
anonimo de capital variable duly organized, validly existing and in good
standing under the laws of Mexico, with all requisite corporate power and
authority to execute and deliver this Agreement and to consummate the
transactions contemplated by this Agreement.

     (c)  Capitalization. The authorized capital stock of the Company consists
of 543,313 shares of common stock, par value $ 1.00 Mexican Peso per share, of
which 543,313 shares are issued and outstanding. The Shares are duly authorized,
validly issued, fully paid and nonassessable.

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

     (e)  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 organizational documents or Bylaws of the
Company or any agreement, indenture or other instrument under which the Company
is bound or to which the Shares or any of the assets of the Company are subject,
or result in the creation or imposition of any security interest, lien, charge
or encumbrance upon the Shares or any of the assets of the Company, or (ii)
violate or conflict with any judgment, decree, order, statute, rule or

                                       4
<PAGE>

regulation of any court or any public, governmental or regulatory agency or body
having jurisdiction over the Company, or the Shares or the assets of the
Company.

     (f)  Consents. To the knowledge of Seller, except as indicated as
conditions precedent to closing in Section 6(c) of this Agreement, or those that
may be required in order to effect the Majority Shareholder Closing described in
Section 6(a) of this Agreement, there are no consents, authorizations, approvals
of, nor is there any governmental or public body or authority 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 on the part of the Seller.

     (g)  Assets and Liabilities. To the knowledge of the Seller, the balance
sheet of the Company provided as Exhibit 7(g) of this Agreement is true
                                 ------------
and complete and fairly reflects the assets and liabilities of the Company as of
the date of this Agreement, except that the Company also owns the Long Distance
License, a value added services license granted on November 28, 1994, and a data
transmission license granted on November 28, 1994, and the Company's liabilities
include an interconnection project involving Telefonos de Mexico, S.A. de C.V.
and Telefonos de Noroeste, S.A. de C.V. as provided in COFETEL's resolution
dated May 28, 1997. The Parties agree that the liability for $31,584 to Comsat
Mexico, S.A. de C.V. is paid as part of the Purchase Price

     (h)  Litigation. Other than those that may be required to obtain the
consents necessary to consummate the transaction contemplated herein, to the
knowledge of the Seller, there are no legal actions or administrative
proceedings or investigations instituted or threatened against the Company. The
Company is not subject to any continuing court or administrative order, writ, or
injunction applicable specifically to the Company or in default with respect
thereto, except as provided in Exhibit 7(n).

     (i)  Employees. To the knowledge of Seller, Exhibit 7(i) hereto contains a
                                                 ------------
complete and accurate list of all employees of the Company as of the date of
this Agreement.

     (j)  Agreements. To the knowledge of Seller, Exhibit 7(j) hereto contains a
                                                  ------------
complete and accurate list of all agreements to which the Company is a party.

     (k)  Officers. To the knowledge of Seller, the individuals serving as
officers of the Company as of the date of this Agreement are shown on Exhibit
                                                                      -------
7(k)
----

     (l)  Agents. To the knowledge of Seller, the Company has not granted a
power of attorney to act on its behalf to any person or authorized any person to
act as an agent of the Company as of the date of this Agreement, except as
otherwise described in Exhibit 7(l).
                       ------------

     (m)  Laws. To the knowledge of the Seller, the Company is in material
compliance with all applicable laws and regulations to which it is subject and
has not failed to file with the proper authorities all necessary statements and
reports required (and

                                       5
<PAGE>

not subject to any exception, exemption or waiver) under such laws and
regulations, except as provided in Section 7(n).

     (n)  Long Distance License. To the knowledge of Seller, except as described
on Exhibit 7(n) or as otherwise permitted under relevant law and regulation the
   ------------
Company is in compliance with the terms of the Long Distance License.

     (o)  Accuracy of Information Furnished. To the knowledge of the Seller, all
information furnished as of the date of this Agreement to Purchaser by Seller in
connection with the transactions contemplated by this Agreement is true, correct
and complete in all material respects. Purchaser acknowledges and agrees that it
has had a full and fair opportunity to investigate the Company and to perform
such investigations as Purchaser has deemed necessary to complete the
transaction contemplated herein.

     8.   Representations and Warranties of Purchaser. ATSI represents and
warrants the following:

     (a)  Organization and Good Standing. Purchaser is a corporation duly
organized, validly existing and in good standing under the laws of the state of
Delaware, 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)  Authorization and Validity. The execution, delivery and performance by
Purchaser of this Agreement and the other agreements contemplated hereby, and
the consummation of the transactions contemplated hereby and thereby, have been
duly authorized by Purchaser. This Agreement and each other agreement
contemplated hereby have been duly executed and delivered by Purchaser and
constitute legal, valid and binding obligations of Purchaser, enforceable
against Purchaser 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.

     (c)  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
Purchaser or any agreement, indenture or other instrument under which Purchaser
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 Purchaser or the properties or assets of
Purchaser.

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

                                       6
<PAGE>

     (e)   Accuracy of Information Furnished. To the knowledge of the Purchaser,
all information furnished as of the date of this Agreement to Seller by
Purchaser in connection with the transactions contemplated by this Agreement is
true, correct and complete in all material respects. Buyer acknowledges and
agrees that it has had a full and fair opportunity to investigate the Company
and to perform such investigations as Purchaser has deemed necessary to complete
the transaction contemplated herein.

     (f)   Assets and Liabilities. The balance sheet of Purchaser provided as
Exhibit 8(f) of this Agreement is true and complete and fairly reflects the
------------
assets and liabilities of the Purchaser as of April 30, 2000.

     (g)   Exemption from Securities Act. Purchaser understands that the Shares
are being transferred by Seller to Purchaser 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
Seller is relying upon the accuracy of, and Seller's compliance with, the
following representations, warranties and covenants to determine the
availability of these exemptions:

     (i)   Purchaser is acquiring the Shares for its 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)  Purchaser is capable, by reason of its business and financial
     experience, of evaluating the relative merits and risks of an investment in
     the Shares, and is able to afford the loss of its investment in the Shares;

     (iii) Purchaser acknowledges that in making its decision to acquire the
     Shares, it has been given an opportunity to ask questions of and to receive
     answers from the Seller's executive officers, directors and management
     personnel concerning the Seller and the Shares;

     (iv)  Purchaser understands that the Shares have not been approved or
     disapproved by the United States Securities and Exchange Commission or any
     state securities commission or the relevant securities regulatory
     authorities of Mexico and that the foregoing authorities have not reviewed
     any documents or instruments in connection with the transfer to Purchaser
     of the Shares and have not confirmed or determined the adequacy or accuracy
     of any such documents or instruments.

     (v)   Purchaser understands that that none of the Shares may be offered,
     sold, transferred, pledged, hypothecated or otherwise disposed of, unless
     registered pursuant to, or exempt from registration under, all applicable
     securities laws (including, as the case may be, U.S. and Mexican law).

     (h)   Purchaser has reviewed the Long Distance License with the assistance
of Mexican regulatory counsel and is familiar with the legal and regulatory
status of the

                                       7
<PAGE>

Long Distance License, including capital increase requirements and the upcoming
deadlines for the start of operations and other matters as required by the SCT
and COFETEL.

9.   Mutual Covenants. Seller covenants to Purchaser, and Purchaser covenants to
Seller the following:

     (a)  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 Purchaser good and marketable title to the Shares, and (ii)
establish and protect the rights created in favor of the parties; including, but
not limited to, seeking additional approval from the SCT, CFCE and the SRE as
described in Sections 6(c) and 9(d) of this Agreement and seeking a further
extension of time for the start of operations from COFETEL if needed, 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

     (b)  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.

     (c)  Best Efforts.  Between the date of this Agreement and the Closing
Date, each Party will use its best efforts to cause the conditions precedent to
their respective obligations to close to be satisfied.

     (d)  Approvals of Governmental Bodies. Within five (5) business days
following the date of this Agreement Purchaser, in coordination with the Seller
shall cause to be made the appropriate notice or filing with the SCT and CFCE in
connection with the transfer of the Shares to ATSI, and the appropriate notice
or filing with the SRE to effect the change in the name of the Company to a name
mutually agreeable to the parties; the parties anticipate that the approval of
the SCT will take no more than 90 days from filing, and that the approvals from
the CFCE and SRE will take more than 45 days from filing; Within three (3)
business days from approval of the name change from the SRE, the Purchaser, in
coordination with the Seller, shall cause to be made the appropriate notice or
filing with the SCT to effect the change in the name of the Company to the name
approved by the SRE.

     (e)  Escrow. Within three (3) business days of the satisfaction of the
Purchaser's Conditions Precedent to Release of Escrow defined in Section 6 of
this Agreement or waiver of those conditions by mutual agreement of the parties,
Purchaser will execute the Release of Escrow in the form attached as Exhibit A
                                                                     ---------
to the Escrow Agreement and transmit it to the Escrow Agent with a copy to
Seller. Promptly upon receipt of the Release of Escrow executed by the Seller,
Seller will execute the Release of Escrow in the form attached as Exhibit A to
                                                                  ---------
the Escrow Agreement and transmit it to the Escrow Agent with a copy to
Purchaser. Purchaser will pay the Escrow Agent's fees under this Agreement. In
the event that COFETEL may establish a later date for the start

                                       8
<PAGE>

of operations under the Long Distance License, execute a joint instruction to
the Escrow Agent that the Escrow Termination Date is changed to that later date.

10.  Indemnification.

     (a)  Indemnification by Seller. Until the date that is one (1) year
following the Closing Date, Seller agrees to indemnify, defend and hold
Purchaser, and each of their respective directors, officers, harmless from and
against all losses, claims, obligations, demands, assessments, penalties,
liabilities, costs, damages, attorneys' fees and expenses (collectively,
"Damages") incurred by Seller by reason of or resulting from a material breach
of this Agreement by Seller, including a breach of any representation, warranty,
or covenant made by Seller herein; provided that in no case shall the aggregate
amount of Seller's obligation to indemnify Purchaser hereunder exceed the
consideration received by Seller as the purchase price hereunder.

     (b)  Indemnification by Purchaser. Until the date that is one (1) year
following the Closing Date, Purchaser agrees to indemnify defend and hold Seller
and its respective directors and officers, harmless from and against all Damages
asserted against or incurred by them by reason of or resulting from an actual or
asserted breach of this Agreement by ATSI, including a material breach of this
Agreement, including a breach of any representation, warranty or covenant made
by Purchaser herein.

     (c)  Procedures. A person seeking indemnification under this Section
shall provide prompt notice of its claim for indemnification to the indemnifying
party. The indemnifying person will have the right to select counsel and to
defend the claim in respect of any indemnified matter under this Section. The
indemnifying party will keep the indemnified party informed of the status of any
litigation or dispute resolution procedure, will give reasonable consideration
to the suggestions and requests of the indemnified party with respect to the
conduct of the litigation or dispute resolution procedure. The indemnified party
will cooperate in the defense of the claim and shall provide such information as
the indemnifying party may reasonably require to defend the claim. The
indemnified party shall not settle any matter covered by this Section without
the prior consent of the indemnifying party. Amounts due under this section
shall be paid upon final resolution of the underlying claim, and may be offset
against amounts due the indemnifying party under this Agreement if not paid
promptly.

11.  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, without the consent of the other
Party (which shall not be unreasonably withheld), except by either Party to an
affiliate of such Party or by Seller to Lockeed Martin Corporation of any of its
affiliates; provided that affiliate shall mean any

                                       9
<PAGE>

entity that controls, is controlled by or is under common control of an entity
that controls such Party.

     (c)  Survival. The provisions of Sections 7 and 8 shall survive the closing
of the transactions contemplated by this Agreement and shall continue for a
period of one (1) year.

     (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.

     (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 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 REQUIRED MEXICAN

                                       10
<PAGE>

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. Confidential
Information shall include any of the terms, conditions or other facts with
respect to the transactions contemplated by this Agreement, including the status
thereof. 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)  Publicity. Neither Party's Representative shall (i) make any public
announcement, release or disclosure, written or otherwise, regarding the terms
of this Agreement or (ii) use the name "COMSAT," "CI," "COMSAT International,"
"Communications Satellite Corporation," or any derivative or variation thereof
without the prior written consent of COMSAT International.

     (k)  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.

     (l)  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.

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

                                       11
<PAGE>

     (n)  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 Purchaser:    American TeleSource International, Inc.
                         6000 Northwest Blvd, 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 Seller:       COMSAT Mexico, S.A. de C.V.
                         Ave. Renato Leduc No. 321
                         Col. Toriello Guerra 14050
                         Mexico, D.F.
                         Telephone: (525) 528-2100
                         Facsimile: (525) 528-2321

     with a copy to:     Office of the General Counsel
                         COMSAT International
                         6560 Rock Spring Drive
                         Bethesda, MD 20817
                         Telephone: (310)214-3611
                         Facsimile: (310)214-7128

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

     (o)  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

                                       12
<PAGE>

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.

     (p)  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.

     (q)  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

                                       13
<PAGE>

          EXECUTED as of the date first above written.

                                        AMERICAN TELESOURCE
                                        INTERNATIONAL, INC.

                                        By:   ______________________________
                                        Name: Arthur L. Smith
                                        Its:  Chief Executive Officer
                                        Date: June 6, 2000

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

                                        By:   ______________________________
                                        Name: Mary Gramaglia
                                              Attorney-in-Fact
                                        Date: June 6, 2000

Exhibits

1          Escrow Agreement
4(f)-1     Officer's Certificate - COMSAT Mexico
4(f)-2     Secretary's Certificate - COMSAT Mexico
4(g)-1     Officer's Certificate - ATSI
4(g)-2     Secretary's Certificate - ATSI
7(g)       Company balance sheet
7(i)       Company employees
7(j)       Company material agreements
7(k)       Company officers
7(l)       Company powers of attorney
7(n)       Exceptions to compliance with Long Distance License
8(f)       Purchaser's balance sheet

                                       14
<PAGE>

                                   Exhibit 1

Escrow Agreement

                                       15
<PAGE>

                                Exhibit 4(f)-1

Officer's Certificate - COMSAT Mexico

                                       16
<PAGE>

                                Exhibit 4(f)-2

Secretary's Certificate - COMSAT Mexico

                                       17
<PAGE>

                                 Exhibit 4(g)

Officer's Certificate - ATSI

                                       18
<PAGE>

                                 Exhibit 7(g)

Balance Sheet of Grupo Intelcom

                                       19
<PAGE>

                       Exhibit 7(i) - Company Employees

None.

                                       20
<PAGE>

                  Exhibit 7(j) - Company Material Agreements

Surety Bonds executed with Afianzadora Mexicana, S.A. and Fianzas Monterrey
Aetna, S.A.

                                       21
<PAGE>

                         Exhibit 7(k)-Company Officers

None.

                                       22
<PAGE>

                   Exhibit 7(l) - Company Powers of Attorney

None.

                                       23
<PAGE>

             Exhibit 7(n) - Compliance with Long Distance License

None. Previous conditions of non-compliance cured by extension of time to meet
concession requirements granted by COFETEL Resolution
#CFT/D06/CGST/DGLDVA/02251/2000, including upcoming deadlines for start of
operations.

                                       24
<PAGE>

                                 Exhibit 8(f)

ATSI Balance Sheet for month ending April 30, 2000.

                                       25

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