Document:

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                                                                    EXHIBIT 10.5

                             SUBSCRIPTION AGREEMENT

                                   dated as of

                                January 31, 2000

                                     between

                            IMPSAT FIBER NETWORKS INC.

                                       and

                                NUNSGATE LIMITED

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                             SUBSCRIPTION AGREEMENT

            SUBSCRIPTION AGREEMENT, dated as of January 31, 2000, between IMPSAT
Fiber Networks, Inc., a Delaware corporation (the "Issuer") and Nunsgate
Limited, a wholly owned Subsidiary of British Telecommunications plc, (the
"Purchaser").

            WHEREAS, the Issuer desires to issue, sell and deliver to the
Purchaser 2,850,000 shares of Common Stock, par value $0.01 per share (the
"Shares"), upon the terms and conditions set forth in this Agreement;

            WHEREAS, the Purchaser desires to subscribe for the Shares from the
Issuer upon the terms and conditions set forth in this Agreement; and

            WHEREAS, on the Closing Date, for good and valuable consideration,
the Issuer shall issue to the Purchaser the Shares upon the terms and conditions
set forth in this Agreement;

            NOW, THEREFORE, in consideration of the mutual covenants, promises
and agreements herein contained, the parties hereto do hereby bind themselves
and agree as follows:

                                   ARTICLE I

                                   DEFINITIONS

        SECTION 1.01.  Definitions.

            (a) In addition to terms defined elsewhere herein, the following
terms, as used herein, have the following meanings:

            "Affiliate" has the meaning assigned to such term by Rule 144 under
the Securities Act.

            "Business Day" means any day that is not a Saturday, a Sunday or
other day on which banks are required or authorized by Law to be closed in the
City of New York.

            "Bylaws" means the Bylaws of the Issuer in effect as of the date
hereof.

            "Charter" means the Certificate of Incorporation of the Issuer in
effect as of the date hereof.

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            "Common Stock" means the common stock, par value $0.01 per share, of
the Issuer.

            "Governmental Authority" means any United States federal, state or
local or any foreign government, governmental, regulatory or administrative
authority, agency or commission or any court, tribunal, or judicial or arbitral
body.

            "Governmental Authorization" shall mean any approval, authorization,
permit, order, consent, exemption or license or any other action of or by, or
notice to or filing or registration with any agencies, departments, ministries,
authorities, statutory or public corporations or other statutory bodies, now
existing or hereinafter created of the United States, the United Kingdom or the
Republic of Argentina, or of any state, municipality or other political
subdivision thereof.

            "Law" means any United States federal, state, local or foreign
statute, law, ordinance, regulation, rule, code, order or other requirement or
rule of law.

            "Material Adverse Change" means a material adverse change, or any
event, occurrence, state of circumstances or facts or development involving a
prospective material adverse change, in the business, operations, assets,
condition (financial or otherwise), results of operations, properties, assets,
value or prospects of the Issuer and its Subsidiaries taken as a whole.

            "Material Adverse Effect" means a material adverse effect, or any
event, occurrence, state of circumstances or facts or development involving a
prospective material adverse effect, on the business, operations, assets,
condition (financial or otherwise), results of operations, properties, assets,
value or prospects of any specified Person.

            "Initial Public Offering" means the Issuer's initial public offering
of 11,500,000 shares of Common Stock.

            "Person" means an individual, partnership, corporation, business
trust, joint stock company, limited liability company, unincorporated
association, joint venture or any other entity or organization, whether or not a
legal entity, including, without limitation, a government or political
subdivision or an agency or instrumentality thereof.

            "Prospectus" means the prospectus that forms part of the
Registration Statement.

            "Purchase Price" means the U.S. dollar amount equal to the product
of (i) the number of shares of Common Stock comprising the Shares and (ii) the
price per share of Common Stock offered to the public initially pursuant to the
Initial Public Offering.

            "Regulation D" means Regulation D under the Securities Act.

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            "Registration Statement" means the Issuer's registration statement
on Form S-1 filed with the Securities and Exchange Commission (file no.
333-88389) relating to the Common Stock to be issued in the Initial Public
Offering, as amended or supplemented at the time it becomes effective.

            "Securities Act" means the U.S. Securities Act of 1933, as amended
from time to time, or any successor statute.

            "Securityholders Agreement" means the Securityholders Agreement,
dated as of March 19, 1998, among the Issuer, Nevasa Holdings Ltd., Princes Gate
Investors II, L.P., Morgan Stanley Global Emerging Markets Private Investment
Fund, L.P., and certain other parties thereto.

            "Shareholders Agreement" means the Shareholders Agreement dated as
of March 10, 1999 among the Issuer, the Purchaser and Nevasa Holdings Ltd.

            "Subsidiary" means, with respect to any Person, any other Person of
which more than fifty percent (50%) of (i) the economic interest in the assets,
earnings or cash flow or (ii) the total voting power of shares of capital stock
entitled (without regard to the occurrence of any contingency) to vote in the
election of directors, managers or trustees thereof, is at the time owned or
controlled, directly or indirectly, by such Person or one or more of the other
Subsidiaries of such Person or a combination thereof.

            "Underwriter" means each Person identified in the Prospectus as an
underwriter in connection with the Initial Public Offering.

            (b)   Each of the following terms is defined in the Section opposite
such term:

<TABLE>
<CAPTION>
Term                            Section
----                            -------
<S>                             <C>
Closing                         2.03
Closing Date                    2.03
Damages                         7.03
Environmental Laws              3.17
Indemnified Persons             7.03
Intellectual Property Rights    3.23
Issuer                          Recitals
Issuer Indemnified Person       7.03
Purchaser                       Recitals
Purchaser Indemnified Person    7.03
Shares                          Recitals
</TABLE>

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                                   ARTICLE II

                         ISSUANCE AND TRANSFER OF SHARES

        SECTION 2.01.  Issuance and Transfer of Shares.

            Subject to the terms and conditions set forth in this Agreement,
upon the Closing (as defined in Section 2.03 below), (i) the Issuer shall issue,
sell and deliver to the Purchaser certificates evidencing the Shares and full
and complete right, title and interest in and to all of the Shares free and
clear of all claims, liens, charges, encumbrances or rights of third parties of
any nature whatsoever, and (ii) the Purchaser shall subscribe for, receive and
accept the Shares.

        SECTION 2.02.  Consideration for the Shares.

            The aggregate consideration for the Shares shall be the Purchase
Price, which shall be payable in accordance with Section 2.03 below.

        SECTION 2.03.  The Closing.

            (a) Upon the terms and subject to the conditions set forth in this
Agreement, the consummation of the transactions contemplated by this Agreement
(the "Closing") shall take place at the offices of Arnold & Porter, 399 Park
Avenue, New York, New York 10022, at 10:00 a.m. on February 4, 2000, or on such
other date and at such other location as the Issuer and the Purchaser shall
agree. The date and time of the Closing are referred to herein as the "Closing
Date."

            (b) At the Closing, the Purchaser shall pay and deliver the Purchase
Price to the Issuer in U.S. dollars by wire transfer, or by such other method
mutually agreeable to the parties, of immediately available funds to such bank
account designated in writing by the Issuer.

            (c) At the Closing, the Purchaser shall receive one or more duly
executed share certificates in definitive form, registered in the name of the
Purchaser, evidencing the Shares being issued to the Purchaser hereunder.

            (d) In the event that the Closing shall not have occurred by
February 11, 2000, the Issuer or the Purchaser shall be entitled to terminate
this Agreement by written notice to the other party hereto without any liability
to the other party hereto, except to the extent that the failure to consummate
the transactions contemplated arises out of or results from the failure of the
party seeking to terminate this Agreement to perform or observe the covenants
and agreements of such party set forth herein.

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                                  ARTICLE III

              REPRESENTATIONS AND WARRANTIES RELATING TO THE ISSUER

            The Issuer represents and warrants to the Purchaser as follows:

        SECTION 3.01.  Organization, Standing, Etc.

            (a) The Issuer has been duly incorporated, is validly existing as a
corporation in good standing under the Laws of the jurisdiction of its
incorporation, has the corporate power and authority to own its property and to
conduct its business as described in the Prospectus and is duly qualified to
transact business and is in good standing in each jurisdiction in which the
conduct of its business or its ownership or leasing of property requires such
qualification, except to the extent that the failure to be so qualified or be in
good standing would not have a Material Adverse Effect on the Issuer and its
Subsidiaries taken as a whole. All of the shares of capital stock of the
Issuer's Subsidiaries owned by the Issuer have been duly and validly authorized
and issued, are fully paid and non-assessable and are owned by the Issuer, free
and clear of all liens, encumbrances, equities or claims.

            (b) Each Subsidiary of the Issuer has been duly incorporated, is
validly existing under the Laws of the jurisdiction of its incorporation, has
the corporate power and authority to own its property and to conduct its
business as described in the Prospectus and is duly qualified to transact
business in each jurisdiction in which the conduct of its business or its
ownership or leasing of property requires such qualification, except to the
extent that the failure to be so qualified would not have a Material Adverse
Effect on such Subsidiary. IMPSAT S.A. ("IMPSAT Argentina") is a 95.2% owned
Subsidiary of the Issuer, IMPSAT S.A. ("IMPSAT Colombia") is a 74.2% owned
Subsidiary of the Issuer, Impsatel del Ecuador S.A. is a wholly owned Subsidiary
of the Issuer, IMPSAT S.A. de C.V. is a 99.9% owned Subsidiary of the Issuer,
Telecomunicaciones IMPSAT S.A. ("IMPSAT Venezuela") is a 75% owned Subsidiary of
the Issuer, and IMPSAT Comunicacoes Ltda. is a 99.9% owned Subsidiary of the
Issuer. As of the Closing Date, IMPSAT Argentina, IMPSAT Colombia and IMPSAT
Venezuela will each be a wholly owned Subsidiary of the Issuer, and the Issuer's
ownership interest in its other Subsidiaries as identified in the preceding
sentence will be unchanged.

        SECTION 3.02.  Registration Statement and Prospectus.

            (a) The Registration Statement, as amended or supplemented, if
applicable, as of the date hereof does not and, when it becomes effective, will
not contain any untrue statement of a material fact or omit to state a material
fact required to be stated therein or necessary to make the statements therein
not misleading.

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            (b) The Prospectus does not contain and, as amended or supplemented,
if applicable, will not contain any untrue statement of a material fact or omit
to state a material fact necessary to make the statements therein, in the light
of the circumstances under which they were made, not misleading, except that the
representations and warranties set forth in this paragraph do not apply to
statements or omissions in the Registration Statement or the Prospectus, both,
as amended or supplemented, if applicable, based upon information relating to
any furnished to the Issuer in writing by such Underwriter expressly for use
therein.

        SECTION 3.03.  Authorization; Capitalization; Non-Contravention.

            (a)   This Agreement has been duly authorized, executed and
delivered by the Issuer.

            (b) The authorized, issued and outstanding capital stock of the
Issuer conforms to the description thereof contained in the Prospectus. The
shares of Common Stock outstanding prior to the issuance of the Shares have been
duly authorized and are validly issued, fully paid and nonassessable. The Shares
have been duly authorized and, when issued and delivered in accordance with the
terms of this Agreement, will be validly issued, fully paid and nonassessable,
and the issuance of such Shares will not be subject to any preemptive or similar
rights.

            (c) The execution and delivery by the Issuer of, and the performance
by the Issuer of its obligations under, this Agreement will not contravene any
provision of applicable Law, the Charter or Bylaws of the Issuer, as amended to
date, any agreement or other instrument binding upon the Issuer or any of its
Subsidiaries that is material to the Issuer and its Subsidiaries, taken as a
whole (except to the extent that any such contravention would not have a
Material Adverse Effect on the Issuer and its Subsidiaries, taken as a whole),
or any judgment, order or decree of any governmental body, agency or court
having jurisdiction over the Issuer or any Subsidiary; and no consent, approval,
authorization or order of, or qualification with, any governmental body or
agency is required for the performance by the Issuer of its obligations under
this Agreement, except for any consents, approvals, authorizations, orders or
qualifications, the failure to obtain which would not have a Material Adverse
Effect on the ability of the Issuer to perform its obligations under this
Agreement.

        SECTION 3.04.  Binding Effect. Except as limited by applicable
bankruptcy, insolvency, reorganization, moratorium and similar Laws affecting
the enforcement of creditors' rights generally, this Agreement constitutes a
valid and binding agreement of the Issuer, enforceable against the Issuer in
accordance with its terms.

        SECTION 3.05.  Registration Rights. Except as disclosed in the
Registration Statement and the Prospectus, there are no contracts, agreements or
understandings between the Issuer and any Person granting such Person the right
to require the Issuer to file a registration statement under the Securities Act
with respect to any securities of the

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Issuer or to require the Issuer to include such securities with the Shares
registered pursuant to the Registration Statement (or any such right has been
waived).

        SECTION 3.06.  Litigation, Proceedings. There are no legal or
governmental proceedings pending or, to the knowledge of the Issuer, threatened
to which the Issuer or any of its Subsidiaries is a party or to which any of the
properties of the Issuer or any of its Subsidiaries is subject that are required
to be described in the Registration Statement or the Prospectus and are not so
described, or any statutes, regulations, contracts or other documents that are
required to be described in the Registration Statement or the Prospectus or to
be filed as exhibits to the Registration Statement that are not described or
filed as required, except to the extent that such proceeding, statute,
regulation, contract or other document is not reasonably likely to have a
Material Adverse Effect on the Issuer and its Subsidiaries, taken as a whole.

        SECTION 3.07.  Disclosure.

            (a) The Issuer has provided the Purchaser with all the information
available to it that the Purchaser has requested for determining whether to
purchase the Shares. Neither this Agreement nor any other written statements or
certificates made or delivered by the Issuer to the Purchaser in connection
herewith contains any untrue statement of a material fact or omits to state a
material fact necessary to make the statements herein and therein not
misleading.

        SECTION 3.08.  Offerings. Assuming the accuracy of the representations
of the Purchaser set forth in Section 4.06 hereof, the offer and transfer of the
Shares to the Purchaser as contemplated by this Agreement are, and would be,
exempt from the registration requirements of the Securities Act.

        SECTION 3.09.  Investment Company.  The Issuer is not, and after
giving effect to the sale and issuance of the Shares will not be, required to
register as an "investment company" under the Investment Company Act of 1940, as
amended.

        SECTION 3.10.  Solicitation; Access to Information. No form of general
solicitation or general advertising was used by the Issuer or, to the Issuer's
knowledge, any other Person acting on its behalf, in respect of the Shares or in
connection with the offer and sale of the Shares.

        SECTION 3.11.  Absence of Certain Changes.  There has not occurred
any Material Adverse Change not set forth in the Prospectus (exclusive of any
amendments or supplements thereto subsequent to the date of this Agreement).

        SECTION 3.12.  Properties. The Issuer and its Subsidiaries have good and
marketable title in fee simple to all real property and good title to all
personal property owned by them which is material to the business of the Issuer
and its Subsidiaries, taken as a whole, in each case free and clear of all
liens, encumbrances and defects except such as are described in the Prospectus
or such as do not materially affect the value of such

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property and do not materially interfere with the use made and proposed to be
made of such property by the Issuer and its Subsidiaries; and any real property
and buildings held under lease by the Issuer and its Subsidiaries are held by
them under valid, subsisting and enforceable leases with such exceptions as are
not material and do not materially interfere with the use made and proposed to
be made of such property and buildings by the Issuer and its Subsidiaries, in
each case except as described in the Prospectus.

        SECTION 3.13.  Internal Controls. The Issuer and each of its
Subsidiaries keep accurate books and records reflecting their assets and
maintain a system of internal accounting controls sufficient to provide
reasonable assurance that (i) transactions are executed in accordance with
management's general or specific authorizations; (ii) transactions are recorded
as necessary to permit preparation of consolidated financial statements in
conformity with generally accepted accounting principles and to maintain asset
accountability; (iii) access to assets is permitted only in accordance with
management's general or specific authorization; and (iv) the recorded
accountability for assets is compared with the existing assets at reasonable
intervals and appropriate action is taken with respect to any differences.

        SECTION 3.14.  Employees. No material labor dispute with the employees
of the Issuer or any of its Subsidiaries exists, except as described in or
contemplated by the Prospectus, or, to the knowledge of the Issuer, is imminent;
and the Issuer is not aware of any existing, threatened or imminent labor
disturbance by the employees of any of its principal suppliers, manufacturers or
contractors that could have a Material Adverse Effect on the Issuer and its
Subsidiaries, taken as a whole.

        SECTION 3.15.  No Undisclosed Material Liabilities. Subsequent to the
respective dates as of which information is given in the Registration Statement
and the Prospectus, the Issuer and its Subsidiaries have not incurred any
material liability or obligation, direct or contingent, nor entered into any
material transaction not in the ordinary course of business.

        SECTION 3.16.  Intellectual Property. The Issuer and its Subsidiaries
own or possess, or can acquire on reasonable terms, all material patents, patent
rights, licenses, inventions, copyrights, know-how (including trade secrets and
other unpatented and/or unpatentable proprietary or confidential information,
systems or procedures), trademarks, service marks and trade names currently
employed by them in connection with the business now operated by them, and,
except as described in the Prospectus, neither the Issuer nor any of its
Subsidiaries has received any notice of infringement of or conflict with
asserted rights of others with respect to any of the foregoing which, singly or
in the aggregate, if the subject of an unfavorable decision, ruling or finding,
would have a Material Adverse Effect on the Issuer and its Subsidiaries, taken
as a whole.

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        SECTION 3.17.  Environmental Compliance.

            (a) The Issuer and its Subsidiaries (i) are in compliance with any
and all applicable Laws relating to the protection of human health and safety,
the environment or hazardous or toxic substances or wastes, pollutants or
contaminants ("Environmental Laws"), (ii) have received all permits, licenses or
other approvals required of them under applicable Environmental Laws to conduct
their respective businesses and (iii) are in compliance with all terms and
conditions of any such permit, license or approval, except where such
noncompliance with Environmental Laws, failure to receive required permits,
licenses or other approvals or failure to comply with the terms and conditions
of such permits, licenses or approvals would not, singly or in the aggregate,
have a Material Adverse Effect on the Issuer and its Subsidiaries, taken as a
whole.

            (b) There are no costs or liabilities associated with Environmental
Laws (including, without limitation, any capital or operating expenditures
required for cleanup, closure of properties or compliance with Environmental
Laws or any permit, license or approval, any related constraints on operating
activities and any potential liabilities to third parties) which would, singly
or in the aggregate, have a Material Adverse Effect on the Issuer and its
Subsidiaries, taken as a whole.

        SECTION 3.18.  Insurance. The Issuer and each of its Subsidiaries are
insured by insurers of recognized financial responsibility against such losses
and risks and in such amounts as the Issuer reasonably believes are prudent and
customary in the businesses in which they are engaged; neither the Issuer nor
any such Subsidiary has been refused any insurance coverage sought or applied
for; and neither the Issuer nor any such Subsidiary has any reason to believe
that it will not be able to renew its existing insurance coverage as and when
such coverage expires or to obtain similar coverage from similar insurers as may
be necessary to continue its business at a cost that would not have a Material
Adverse Effect on the Issuer and its Subsidiaries, taken as a whole, except as
described in the Prospectus.

        SECTION 3.19.  Year 2000. The Issuer has reviewed its operations and
that of its Subsidiaries to evaluate the extent to which the business or
operations of the Issuer or any of its Subsidiaries will be affected by the Year
2000 Problem (that is, any significant risk that computer hardware or software
applications used by the Issuer and its Subsidiaries will not, in the case of
dates or time periods occurring after December 31, 1999, function at least as
effectively as in the case of dates or time periods prior to January 1, 2000);
as a result of such review, (i) the Issuer has no reason to believe, and does
not believe, that (A) there are any issues related to the Issuer's preparedness
to address the Year 2000 Problem that are of a character required to be
described or referred to in the Registration Statement or Prospectus which have
not been accurately described in the Registration Statement or Prospectus and
(B) the Year 2000 Problem will have a Material Adverse Effect on the Issuer and
its Subsidiaries, taken as a whole, or result in any material loss or
interference with the business or operations of the Issuer and its Subsidiaries,
taken as a whole; (ii) the Issuer reasonably believes, after due inquiry, that
the suppliers, vendors,

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customers or other material third parties used or served by the Issuer and such
Subsidiaries are addressing or will address the Year 2000 Problem in a timely
manner, except to the extent that a failure to address the Year 2000 Problem by
any supplier, vendor, customer or material third party would not have a Material
Adverse Effect on the Issuer and its Subsidiaries, taken as a whole; and (iii)
nothing has come to the attention of the Issuer as of the date hereof, after due
inquiry, that any Year 2000 Problems have occurred that (A) could have a
Material Adverse Effect on the Issuer and its Subsidiaries, taken as a whole, or
result in any material loss or interference with the business or operations of
the Issuer and its Subsidiaries, taken as a whole or (B) are of a character
required to be described or referred to in the Registration Statement or
Prospectus which have not been accurately described in the Registration
Statement or Prospectus.

                                   ARTICLE IV

                 REPRESENTATIONS AND WARRANTIES OF THE PURCHASER

        The Purchaser represents and warrants to the Issuer as follows:

        SECTION 4.01.  Organization.  The Purchaser is duly organized and
existing under the Laws of its jurisdiction of organization.

        SECTION 4.02.  Authority; No Other Action.

            (a) The execution, delivery and performance of this Agreement is
within the Purchaser's powers and have been duly authorized on the Purchaser's
part by all requisite corporate action.

            (b) No action by or in respect of, or filing with, any Governmental
Authority is required for the execution, delivery and performance by the
Purchaser of this Agreement.

        SECTION 4.03.  No Contravention. The execution, delivery and performance
by the Purchaser of this Agreement and the consummation of the transactions
contemplated hereby do not and will not (i) violate the Purchaser's charter or
similar document or (ii) violate any applicable Law, judgment, injunction or
decree, which violation would (a) affect the validity of this Agreement or (b)
individually or in the aggregate impair the ability of the Purchaser to perform
in any material respect its obligations under this Agreement.

        SECTION 4.04.  Binding Effect. Except as limited by applicable
bankruptcy, insolvency, reorganization, moratorium and similar Laws affecting
the enforcement of creditors' rights generally, this Agreement has been duly
executed by the Purchaser and constitutes a valid and binding agreement of the
Purchaser.

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        SECTION 4.05.  No Defaults. The Purchaser is not in violation of its
charter or in default under any provision of applicable Law or of any agreement,
judgment, injunction, decree or other instrument binding upon it, which
violation or default (i) would affect the validity of this Agreement or (ii)
would (individually or in the aggregate) impair the ability of the Purchaser to
perform in any material respect its obligations under this Agreement.

        SECTION 4.06.  Private Placement.

            (a) The Purchaser understands that (i) the offering and sale of the
Shares is intended to be exempt from registration under the Securities Act
pursuant to Section 4(2) of the Securities Act, (ii) the Shares are not
registered under the Securities Act and (iii) there is no existing public or
other market for the Shares and there can be no assurance that the Purchaser
will be able to sell or dispose of the Shares.

            (b)   The Purchaser is an "Accredited Investor" as such term is
defined in Regulation D.

            (c) The Purchaser has sufficient knowledge and experience in
financial and business matters so as to be capable of evaluating the merits and
risks of its investment in the Shares and is capable of bearing the economic
risks of such investment.

                                   ARTICLE V

                                    COVENANTS

        SECTION 5.01.  Regulatory and Other Authorization; Consents. (a) Each of
the Issuer and the Purchaser shall use all reasonable efforts to obtain all
authorizations, consents, orders and approvals of all Governmental Authorities
that may be or become necessary for its execution and delivery of, and the
performance of its obligations pursuant to, this Agreement and will cooperate
fully with each other in promptly seeking to obtain all such authorizations,
consents, orders and approvals.

            (b) The Issuer shall give promptly such notices to third parties and
use all its or their reasonable efforts to obtain such third party consents as
are necessary in connection with the transactions contemplated by this
Agreement.

            (c) Each of the Issuer and the Purchaser shall cooperate and use all
reasonable efforts to assist each other in giving such notices and obtaining
such consents; provided, however, that the Purchaser shall not have any
obligation to give any guarantee or other consideration of any nature in
connection with any such notice or consent or to consent to any change in the
terms of any agreement or arrangement which the Purchaser in its sole and
absolute discretion may deem adverse to the interests of the Purchaser, the
Issuer or any Subsidiary of the Issuer.

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            (d) Each of the Issuer and the Purchaser believes that all the
consents, approvals and authorizations necessary for the consummation of the
transactions contemplated hereby will be received.

        SECTION 5.02.  Further Action. Each of the Issuer and the Purchaser
shall use all reasonable efforts to take, or cause to be taken, all appropriate
action, do or cause to be done all things necessary, proper and advisable under
applicable Law, and execute and deliver such documents and other papers, as may
be required to carry out the provisions of this Agreement and consummate and
make effective the transactions contemplated by this Agreement.

                                   ARTICLE VI

                         CONDITIONS PRECEDENT TO CLOSING

        SECTION 6.01.  Conditions to the Purchaser's Obligations.  The
obligation of the Purchaser to purchase the Shares from the Issuer is subject to
the satisfaction, on or prior to the Closing Date, of the following conditions:

            (a) each of the representations and warranties of the Issuer
contained herein shall be true and correct on and as of the Closing Date;

            (b) the Issuer shall have performed and complied with all covenants
and agreements required by this Agreement to be performed or complied with by
the Issuer on or prior to the Closing Date, and the Issuer shall not be in
default under or in violation of any provisions of the Charter;

            (c) the Purchaser shall have received a certificate dated the
Closing Date signed by an executive officer of the Issuer to the effect set
forth in subsections (a), (b), and (d) of this Section 6.01;

            (d) the Issuer and the Purchaser shall have obtained all
Governmental Authorizations and all other material consents, waivers or permits,
necessary for the consummation of the transactions contemplated hereby;

            (e) the Purchaser's acquisition of the Shares as provided herein
shall not be prohibited by any applicable Law or any contract, agreement,
document or other instrument by which the Purchaser is bound;

            (f) there shall not have occurred any Material Adverse Change;

            (g) the closing of the Initial Public Offering substantially
concurrently with the Closing;

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            (h) the amendment to the Shareholders Agreement, substantially in
the form attached hereto as Exhibit A, shall have been executed and delivered by
each of the parties thereto; and

            (i) the consent under the Securityholders Agreement, substantially
in the form attached hereto as Exhibit B, shall have been executed and delivered
by each of the parties thereto.

        SECTION 6.02.  Conditions to Issuer's Obligations. The obligations of
the Issuer to issue and sell the Shares to the Purchaser pursuant to this
Agreement are subject to the satisfaction, at or prior to the Closing Date, of
the following conditions:

            (a) the representations and warranties of the Purchaser contained
herein shall be true and correct on and as of the Closing Date;

            (b) the Purchaser shall have performed and complied with all
agreements required by this Agreement to be performed or complied with by the
Purchaser on or prior to the Closing Date;

            (c) the Purchaser's acquisition of the Shares shall not be
prohibited by any applicable Law or any contract, agreement, document or other
instrument by which the Purchaser is bound;

            (d) each of the Issuer and the Purchaser shall have obtained all
Governmental Authorizations and all other material consents, waivers or permits,
necessary for the consummation of the transactions contemplated hereby; and

            (e) the closing of the Initial Public Offering substantially
concurrently with the Closing; and

            (f) the consent under the Securityholders Agreement, substantially
in the form attached hereto as Exhibit B, shall have been executed and delivered
by each of the parties thereto.

                                  ARTICLE VII

                                  MISCELLANEOUS

        SECTION 7.01.  Notices. All notices, requests and other communications
to any party hereunder shall be in writing (including, without limitation,
telecopier or similar writing) and shall be given to such party by certified
first class mail at its address with a return receipt requested, by Federal
Express or similar overnight mail service with signature required for receipt,
or by telecopy at the telecopier number set forth below or such other address or
telecopier number as such party may hereinafter specify in writing

                                       13
<PAGE>   15

for the purpose to the party giving such notice. Each such notice, request or
other communication shall be effective (i) if given by telecopy, when such
telecopy is transmitted to the telecopy number specified in this Section 7.01
and the appropriate electronic confirmation is received and a copy of such
notice is sent by overnight mail service or (ii) if given by certified mail or
overnight courier, 72 hours after such communication is deposited in the mails
with first class postage prepaid or given to overnight courier service,
addressed as aforesaid.

            Issuer:           IMPSAT Fiber Networks, Inc.
                              Alferez Pareja 256
                              1107 Buenos Aires, Argentina
                              Attn:  Chief Executive Officer
                              Telefax: 011-54-11-4300-8060

            Purchaser:        Nunsgate Limited
                              Queen Victoria House
                              Queen Victoria Street
                              Douglas IM1 2LS
                              Isle of Man
                              Telefax:  011 44 1624 636 011

                              With a copy to:

                              Secretary and Chief Legal Adviser
                              British Telecommunications plc
                              81 Newgate Street
                              London EC1A 7AJ
                              United Kingdom
                              Telefax: 011-44171-356-6135

        SECTION 7.02.       No Waivers; Amendments.

            (a) No failure or delay on the part of any party in exercising any
right, power or privilege hereunder shall operate as a waiver thereof, nor shall
any single or partial exercise thereof preclude any other or further exercise
thereof or the exercise of any other right, power or privilege. The rights and
remedies herein provided shall be cumulative and not exclusive of any rights or
remedies provided by Law.

            (b) Any provision of this Agreement may be amended or waived if, but
only if, such amendment or waiver is in writing and is signed by both parties
hereto.

        SECTION 7.03.       Indemnification.

            (a) The Issuer hereby agrees to indemnify and hold harmless the
Purchaser, its Affiliates and their directors, officers, agents and employees
(each, a

                                       14
<PAGE>   16

"Purchaser Indemnified Person") from and against and to pay any losses,
claims, damages or liabilities (or actions or proceedings in respect thereof)
("Damages") to which such Purchaser Indemnified Person may become subject as the
result of any misrepresentation, breach of representation, warranty or covenant
made or to be performed on the part of the Issuer under this Agreement and will
reimburse any Purchaser Indemnified Person for all reasonable expenses
(including, without limitation, reasonable counsel and expert fees) as they are
incurred by any such Purchaser Indemnified Person in connection with any such
misrepresentation or breach of representation, warranty or covenant or
investigating, preparing or defending any such action or proceeding, whether
pending or threatened, and whether or not such Purchaser Indemnified Person is a
party hereto. The Issuer will not be responsible for any Damages or expenses to
the extent that a court of competent jurisdiction shall have finally determined
that such Damages or expenses resulted primarily from such Purchaser Indemnified
Person's bad faith or breach of this Agreement. The agreement of the Issuer in
this Section 7.03(a) shall be in addition to any liability the Issuer may
otherwise have.

            (b) The Purchaser hereby agrees to indemnify and hold harmless the
Issuer, its Affiliates and their directors, officers, agents and employees
(each, an "Issuer Indemnified Person" and collectively with the Purchaser
Indemnified Persons, the "Indemnified Persons"), from and against and to pay any
Damages to which such Issuer Indemnified Person may become subject as the result
of any misrepresentation, breach of representation, warranty or covenant made or
to be performed on the part of the Purchaser under this Agreement and will
reimburse any Issuer Indemnified Person for all reasonable expenses (including,
without limitation, reasonable counsel and expert fees) as they are incurred by
any such Issuer Indemnified Person in connection with any such misrepresentation
or breach of representation, warranty or covenant or investigating, preparing or
defending any such action or proceeding, whether pending or threatened, and
whether or not such Issuer Indemnified Person is a party hereto. The Purchaser
will not be responsible for any Damages or expenses to the extent that a court
of competent jurisdiction shall have finally determined that such Damages or
expenses resulted primarily from such Issuer Indemnified Person's bad faith or
breach of this Agreement. The agreement of the Purchaser in this Section 7.03(b)
shall be in addition to any liability the Purchaser may otherwise have.

            (c) None of the Issuer nor the Purchaser may make a claim for
indemnification for any sums due under this Article VII until the aggregate
amount of the Damages exceeds U.S.$1.5 million and then, the Damages shall be
limited to in the case of claims against the Issuer to a maximum aggregate
amount of U.S.$20 million; provided that, in the event that the U.S.$1.5 million
threshold is exceeded, any party may assert one or more claims for
indemnification for any and all claims regardless of the amount of such claims
(up to the maximum amount for the Issuer provided for above) and going back to
the first U.S. dollar of such Damages.

            (d) Neither the Issuer nor the Purchaser shall be entitled to
indemnification hereunder with respect to the breach of any warranty,
representation,

                                       15
<PAGE>   17

covenant or agreement contained herein unless such claim for
indemnification is asserted against the party from whom indemnification is
sought within 18 months after the Closing Date. A claim shall be deemed to have
been asserted when notice of such claim is given pursuant to Section 7.01 hereof
in sufficient detail for the nature and substance of the claim to be clear to
the recipients of such notice.

        SECTION 7.04.  Successors and Assigns. The Purchaser may assign its
rights and obligations hereunder to a direct or indirect wholly-owned Subsidiary
of British Telecommunications plc if such Subsidiary becomes a party to this
Agreement without the consent of the Issuer, or to any other Person with the
prior written consent of the Issuer. The Issuer may not delegate its obligations
hereunder. This Agreement shall be binding upon the Issuer and the Purchaser and
their respective successors and assigns.

        SECTION 7.05.  New York Law.  This Agreement shall be construed in
accordance with and governed by the laws of the State of New York.

        SECTION 7.06.  Counterparts; Effectiveness. This Agreement may be
executed in any number of counterparts each of which shall be an original with
the same effect as if the signatures thereto and hereto were upon the same
instrument. This Agreement shall become effective when each party hereto shall
have received a counterpart hereof signed by the other hereto.

        SECTION 7.07.  Entire Agreement. This Agreement constitutes the entire
agreement and understanding of the parties hereto in respect of the subject
matter contained herein and therein, and there are no restrictions, promises,
representations, warranties, covenants, or undertakings with respect to the
subject matter hereof, other than those expressly set forth or referred to
herein or therein.

        SECTION 7.08.  Remedies. The parties hereby acknowledge that money
damages would not be adequate compensation for the damages that a party would
suffer by reason of a failure of any other party to perform any of the
obligations under this Agreement. Therefore, each party hereto agrees that
specific performance is the only appropriate remedy under this Agreement and
hereby waives the claim or defense that any other party has an adequate remedy
at law. No party shall be liable for consequential damages as a result of any
breach hereof.

        SECTION 7.09.  Jurisdiction. Each of the parties hereto agrees that any
legal suit, action or proceeding arising out of or relating to this Agreement or
the transaction contemplated herein may be instituted in any U.S. federal or New
York State court in the Borough of Manhattan in the City of New York or in the
court of the corporate domicile of each of the parties hereto, with respect to
actions brought against that party as a defendant, and each of the parties
hereto hereby waives any objection which it may now or hereafter have to the
laying of venue of any such proceeding, and irrevocably submits to the
jurisdiction of such courts and to the courts of its corporate domicile, with
respect to actions brought against it as defendant, in any suit, action or
proceeding.

                                       16
<PAGE>   18

        SECTION 7.10.  Judgment Currency. If for purposes of obtaining judgment
in any court it is necessary to convert a sum due hereunder into any currency
other than U.S. dollars, the parties hereto agree, to the fullest extent that
they may effectively do so, that the rate of exchange used shall be the rate at
which in accordance with normal banking procedures the Purchaser could purchase
U.S. dollars with such other currency in the City of New York on the Business
Day preceding that on which final judgment is given.

        SECTION 7.11.  Severability. If any term or other provision of this
Agreement is invalid, illegal or incapable of being enforced by any Law or
public policy, all other terms and provisions of this Agreement shall
nevertheless remain in full force and effect so long as the economic or legal
substance of the matters contemplated hereby is not affected in any manner
materially adverse to any party. Upon such determination that any term or other
provision is invalid, illegal or incapable of being enforced, the parties hereto
shall negotiate in good faith to modify this Agreement so as to effect the
original intent of the parties as closely as possible in an acceptable manner in
order that the matters contemplated hereby are consummated as originally
contemplated to the greatest extent possible.

        IN WITNESS WHEREOF, the parties have caused this Agreement to be duly
executed, as of the day and year first above written.

                                    IMPSAT FIBER NETWORKS, INC.

                                    By:
                                       -------------------------------
                                    Name:
                                    Title:

                                    NUNSGATE LIMITED

                                    By:
                                       -------------------------------
                                    Name:
                                    Title:

                                       17
<PAGE>   19

                                    EXHIBIT A

                     AMENDMENT NO.1 TO SHAREHOLDERS AGREEMENT

<PAGE>   20

                                    EXHIBIT B

                CONSENT TO AMENDMENT NO.1 TO SHAREHOLDERS AGREEMENT<PAGE>   1
                                                                     EXHIBIT 4.1

                         Subordinated Loan Agreement

                                   ---------

                                   FORM SL-1

                                   ---------

                NATIONAL ASSOCIATION OF SECURITIES DEALERS, INC.
                  1735 K STREET, N.W., WASHINGTON, D.C. 20006

<PAGE>   2

                                      NASD

                          SUBORDINATED LOAN AGREEMENT

                                      SL-1

                               AGREEMENT BETWEEN:

Lender                         Clark N. Wilson
        ------------------------------------------------------------------------
                                    (Name)

                             5312 Park Hollow Lane
--------------------------------------------------------------------------------
                                (Street Address)

Austin                                             Texas               78746
-------------------------------------------  -------------------  --------------
             (City)                               (State)              (Zip)

                                      AND

Broker-Dealer       Tejas Securities Group, Inc.
              ------------------------------------------------------------------
                                     (Name)

1250 Capital of Texas Highway South Bldg. 2 Suite 500
--------------------------------------------------------------------------------
                                (Street Address)

Austin                                             Texas               78746
-------------------------------------------  -------------------  --------------
             (City)                               (State)              (Zip)

NASD ID NO.:        036705
             -------------------------------------------------------------------

DATE FILED:    October 13, 1998
            --------------------------------------------------------------------

<PAGE>   3

                                      NASD
                          SUBORDINATED LOAN AGREEMENT
                                      upon
                                      NASD
                                    Approval

         AGREEMENT dated 10-13-98 to be effective ____________ between Clark N.
Wilson, (the "Lender") and Tejas Securities Group, Inc. (the "Broker-Dealer")

         In consideration of the sum of $500,000.00 and subject to the terms and
conditions hereinafter set forth, the Broker-Dealer promises to pay to the
Lender or assigns on November 1, 2001, at the principal office of the Broker-
Dealer the aforedescribed sum and interest thereon payable at the rate of 11.5%
percent per annum from the effective date of this Agreement, which date shall be
the date so agreed upon by the Lender and the Broker-Dealer unless otherwise
determined by the National Association of Securities Dealers, Inc. ("NASD").
This Agreement shall not be considered a satisfactory subordination agreement
pursuant to the provisions of 17 CFR 240.15c3-1d unless and until the NASD has
found the Agreement acceptable and such Agreement has become effective in the
form found acceptable.

         The cash proceeds covered by this Agreement shall be used and dealt
with by the Broker-Dealer as part of its capital and shall be subject to the
risks of the business. The Broker-Dealer shall have the right to deposit any
cash proceeds of this Subordinated Loan Agreement in an account or accounts in
its own name in any bank or trust company.

         The Lender irrevocably agrees that the obligations of the Broker-Dealer
under this Agreement with respect to the payment of principal and interest shall
be and are subordinate in right of payment and subject to the prior payment or
provision for payment in full of all claims of all other present and future
creditors of the Broker-Dealer arising out of any matter occurring prior to the
date on which the related Payment Obligation (as defined herein) matures
consistent with the provisions of 17 CFR 240.15c3-1 and 240.15c3-1d, except for
claims which are the subject of subordination agreements which rank on the same
priority as, or are junior to the claim of the Lender under such subordination
agreements.

I.       PERMISSIVE PREPAYMENTS (OPTIONAL)

         At the option of the Broker-Dealer, but not at the option of the
Lender, payment of all or any part of the "Payment Obligation" amount hereof
prior to the Scheduled Maturity Date may be made by the Broker-Dealer only upon
receipt of the prior written approval of the NASD, but in no event may any
prepayment be made before the expiration of one year from the date this
Agreement became effective. No prepayment shall be made if, after giving effect
thereto (and all payments of Payment Obligations under any other subordination
agreements then outstanding, the maturity or accelerated maturity of which are
scheduled to fall due either within six months after the date such prepayment is
to occur or on or prior to the date on which the Payment Obligation hereof is
scheduled to mature, whichever date is earlier), without reference to any
projected profit or loss of the Broker-Dealer, either aggregate indebtedness of
the Broker-Dealer would exceed 1000 percent of its net capital or such lesser
percent as may be made applicable to the Broker-Dealer from time to time by the
NASD, or a governmental agency or self-regulatory body having appropriate
authority, or if the Broker-Dealer is operating pursuant to paragraph (a)(1)(ii)
of 17 CFR 240.15c3-1, its net capital would be less than 5 percent of aggregate
debit items computed in accordance with 17 CFR 240.15c3-3a, or, if registered as
a futures commission merchant, 7 percent of the funds required to be segregated
pursuant to the Commodity Exchange Act and the regulations thereunder, (less the
market value of commodity options purchased by option customers on or subject to
the rules of a contract market, provided, however, the deduction for each option
customer shall be limited to the amount of customer funds in such option
customers account,) if greater, or its net capital would be less than 120
percent of the minimum dollar amount required by 17 CFR 240.15c3-1 or such
greater dollar amount as may be made applicable to the Broker-

NASD FORM SL-1
                                       1
<PAGE>   4
Dealer by the NASD, or a governmental agency or "self-regulatory" body having
appropriate authority.

II.      SUSPENDED REPAYMENTS

         (a) The Payment Obligation of the Broker-Dealer shall be suspended and
shall not mature if, after giving effect to such payment (together with the
payment of any Payment Obligation of the Broker-Dealer under any other
subordination agreement scheduled to mature on or before such Payment
Obligation) the aggregate indebtedness of the Broker-Dealer would exceed 1200
percent of its net capital or such lesser percent as may be made applicable to
the Broker-Dealer from time to time by the NASD, or a governmental agency or
self-regulatory body having appropriate authority, or if the Broker-Dealer is
operating pursuant to paragraph (a)(1)(ii) of 17 CFR 240.15c3-1, its net
capital would be less than 5 percent of aggregate debit items computed in
accordance with 17 CFR 240.15c3-3a, or, if registered as a futures commission
merchant, 6 percent of the funds required to be segregated pursuant to the
Commodity Exchange Act and the regulations thereunder, (less the market value
of commodity options purchased by option customers on or subject to the rules
of a contract market, provided, however, the deduction for each option customer
shall be limited to the amount of customer funds in such option customers
account,) if greater, or its net capital would be less than 120 percent of the
minimum dollar amount required by 17 CFR 240.15c3-1, or such greater dollar
amount as may be made applicable to the Broker-Dealer by the NASD, or a
governmental agency or self-regulatory body having appropriate authority.

IV.      ACCELERATED MATURITY OF THE SUBORDINATION AGREEMENT UPON THE
         OCCURRENCE OF AN EVENT OF ACCELERATION (OPTIONAL)

         By prior written notice delivered to the Broker-Dealer at its
principal office and to the NASD upon the occurrence of any Event of
Acceleration (as defined herein), given no sooner than six months from the
effective date of this Agreement, the Lender may accelerate such Payment
Obligation to the last business day of a calendar month not less than six
months after the receipt of such notice by both the Broker-Dealer and the NASD.
If, upon such accelerated maturity, the Payment Obligation of the
Broker-Dealer is suspended pursuant to paragraph II of this Agreement, and
liquidation of the Broker-Dealer has not commenced on or prior to such
accelerated maturity date, such Agreement shall mature on the day immediately
following such accelerated maturity date and, in any event, the Payment
Obligations of the Broker-Dealer with respect to all other subordination
agreements then outstanding shall also mature at the same time. Events of
Acceleration which may be included shall be limited to:

         (a) Failure to pay interest or any installment of principal on this
Agreement as scheduled;

NASD FORM SL-1                         2
<PAGE>   5
         (b) Failure to pay when due other money obligations of a specified
material amount;

         (c) Discovery that any material, specified representation or warranty
of the broker-dealer which is included in this Agreement and on which this
Agreement was based or continued was inaccurate in a material respect at the
time made; or

         (d) The following specified and clearly measurable event(s), which the
Lender and Broker-Dealer agree (i) is a significant indication that the
financial position of the Broker-Dealer has changed materially and adversely
from agreed upon specified norms; or (ii) could materially and adversely affect
the ability of the Broker-Dealer to conduct its business as conducted on the
effective date of the subordination agreements; or (iii) is a significant
change in the senior management or in the general business conducted by the
Broker-Dealer from the date this Agreement became effective; or (iv) constitute
continued failure to perform agreed-upon covenants included in this Agreement
relating to the maintenance and reporting by the Broker-Dealer of its financial
position or relating to the conduct of its business.

         The events of Acceleration as discussed in paragraphs (a) through (d)
with respect to this Agreement are enumerated below:

-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------

V.       ACCELERATED MATURITY OF THE SUBORDINATION AGREEMENT UPON THE
         OCCURRENCE OF AN EVENT OF DEFAULT (OPTIONAL)

         (a) If the liquidation of the business of the Broker-Dealer has not
already commenced, the Payment Obligation shall mature, together with accrued
interest or compensation, upon the occurrence of an Event of Default, as
hereinafter defined.

         (b) Further, if liquidation of the business of the Broker-Dealer has
not already commenced, the rapid and orderly liquidation of the business of the
Broker-Dealer shall then commence upon the happening of an Event of Default,
and the date of said Event of Default shall be the date on which the Payment
Obligations of the Broker-Dealer with respect to all other subordination
agreements then outstanding shall mature.

         Events of Default which may be included shall be limited to:

(i) The filing of an application by the Securities Investor Protection
Corporation for a decree adjudicating that customers of the Broker-Dealer are
in need of protection under the Securities Investor Protection Act of 1970 and
the failure of the Broker-Dealer to obtain the dismissal of such application
within 30 days;

(ii) The aggregate indebtedness of the Broker-Dealer exceeding 1500 percent of
its net capital or, in the case of a Broker-Dealer which has elected to operate
under paragraph (a)(1)(ii) of 17 CFR 240.15c-1, its net capital computed in

NASD FORM SL-1                         3
<PAGE>   6

accordance therewith is less than 2 percent of its aggregate debit items
computed in accordance with 17 CFR 240.15c3-3a, or, if registered as a futures
commission merchant, 4 percent of the funds required to be segregated pursuant
to the Commodity Exchange Act and the regulations thereunder, (less the market
value of commodity options purchased by option customers on or subject to the
rules of a contract market, provided, however, the deduction for each option
customer shall be limited to the amount of customer funds in such option
customer's account') if greater, throughout a period of 15 consecutive business
days, commencing on the day the Broker-Dealer first determines and notifies the
Lender and the NASD, or the NASD or the Commission first determines and notifies
the Broker-Dealer of such fact;

(iii) Revocation by the Commission of the registration of the Broker-Dealer;

(iv) Suspension by the NASD (without reinstatement within 10 days) or revocation
of the Broker-Dealer's status as a member thereof; and,

(v) Receivership, insolvency, liquidation pursuant to the Securities Investor
Protection Act of 1970 or otherwise, bankruptcy, assignment for the benefit of
creditors, reorganization whether or not pursuant to bankruptcy laws, or any
other marshaling of the assets and liabilities of the Broker-Dealer.

NASD FORM SL-1                         4
<PAGE>   7
VI.      NOTICE OF MATURITY OR ACCELERATED MATURITY

         The Broker-Dealer shall immediately notify the NASD if, after giving
effect to all payments of Payment Obligations under subordination agreements
then outstanding which are then due or mature within six months without
reference to any projected profit or loss of the Broker-Dealer, either the
aggregate indebtedness of the Broker-Dealer would exceed 1200 percent of its net
capital, or in the case of a Broker-Dealer operating pursuant to paragraph
(a)(1)(ii) of 17 CFR 240.15c3-1, its net capital would be less than 5 percent of
aggregate debit items computed in accordance with 17 CFR 240.15c3-3a, or, if
registered as a futures commission merchant, 6 percent of the funds required to
be segregated pursuant to the Commodity Exchange Act and the regulations
thereunder, (less the market value of commodity options purchased by option
customers on or subject to the rules of a contract market, provided, however,
the deduction for each option customer shall be limited to the amount of
customer funds in such option customer's account), if greater, and in either
case, if its net capital would be less than 120 percent of the minimum dollar
amount required by 17 CFR 240.15c3-1, or such greater dollar amount as may be
made applicable to the Broker-Dealer by the NASD, or a governmental agency or
self-regulatory body having appropriate authority.

VII.     BROKER-DEALERS CARRYING THE ACCOUNTS OF SPECIALISTS AND MARKET MAKERS
         IN LISTED OPTIONS

         A Broker-Dealer who guarantees, endorses, carries or clears specialist
or market-maker transactions in options listed an a national securities
exchange or facility of a national securities association shall not permit a
reduction, prepayment or repayment of the unpaid principal amount if the effect
would cause the equity required in such specialist or market-maker accounts to
exceed 1000 percent of the Broker-Dealer's net capital or such percent as may
be made applicable to the Broker-Dealer from time to time by the NASD or a
governmental agency or self-regulatory body having appropriate authority.

VIII.    BROKER-DEALERS REGISTERED WITH CFTC

         If the Broker-Dealer is a futures commission merchant or introductory
broker as that term is defined in the Commodity Exchange Act, the Organization
agrees, consistent with the requirements of 1.17(h) of the regulations of the
CFTC (17 CFR 1.17(h)), that:

(a) Whenever prior written notice by the Broker-Dealer to the NASD is required
pursuant to the provisions of this Agreement, the same prior written notice
shall be given by the Broker-Dealer to (i) the CFTC at its principal office in
Washington, D.C., attention Chief Accountant of Division of Trading and Markets,
and/or (ii) the commodity exchange of which the Organization is a member and
which is then designated by the CFTC as the Organization's designated
self-regulatory organization the "DSRO");

(b) Whenever prior written consent, permission or approval of the NASD is
required pursuant to the provisions of this Agreement, the Broker-Dealer shall
also obtain the prior written consent, permission or approval of the CFTC
(and/or of the DSRO); and,

NASD FORM SL-1                         5
<PAGE>   8
(c) Whenever the Broker-Dealer receives written notice of acceleration of
maturity pursuant to the provisions of this Agreement, the Broker-Dealer shall
promptly give written notice thereof to the CFTC at the address above stated
and/or to the DSRO.

X.       GENERAL

         This Agreement shall not be subject to cancellation by either the
Lender or the Broker-Dealer, and no payment shall be made, nor the Agreement
terminated, rescinded, or modified my mutual consent or otherwise if the effect
thereof would be inconsistent with the requirements of 17 CFR 240.15c3-1 and
240.15c3-1d.

         The Agreement may not be transferred, sold, assigned, pledged, or
otherwise encumbered or otherwise disposed of, and no lien, charge or other
encumbrance may be created or permitted to be created thereon without the prior
written consent of the NASD.

         In the event of the appointment of a receiver or trustee of the
Broker-Dealer or in the event of its insolvency, liquidation pursuant to the
Securities Investor Protection Act of 1970 or otherwise, bankruptcy, assignment
for the benefit of creditors, reorganization whether or not pursuant to
bankruptcy laws, or any other marshaling at the assets and liabilities of the
Broker-Dealer, the Payment Obligation of the Broker-Dealer shall mature, and the
holder hereof shall not be entitled to participate or share, ratably or
otherwise, in the distribution of the assets of the Broker-Dealer until all
claims of all other present and future creditors at the Broker-Dealer, whose
claims are senior hereto, have been fully satisfied.

         The Lender irrevocably agrees that the loan evidenced hereby is not
being made in reliance upon the standing of the Broker-Dealer as a member
organization of the NASD or upon the NASD surveillance of the Broker-Dealer's
financial position or its compliance with the By-Laws, rules and practices of
the NASD. The Lender has made such investigation of the Broker-Dealer and its
partners, officers, directors and stockholders as the Lender deems necessary and
appropriate under the circumstances. The Lender is not relying upon the NASD to
provide any information concerning or relating to the Broker-Dealer and agrees
that the NASD has no responsibility to disclose to the Lander any information
concerning or relating to the Broker-Dealer which it may now, or at any future
time, have.

NASD FORM SL-1                         6
<PAGE>   9

         The term "Broker-Dealer" as used in this Agreement shall include the
broker-dealer, its heirs, executors, administrators, successors, and assigns.

         The term "Payment Obligation" shall mean the obligation of the
Broker-Dealer to repay cash loaned to it pursuant to this Subordinated Loan
Agreement.

         The provisions of this Agreement shall be binding upon the
Broker-Dealer and the Lender and their respective heirs, executors,
administrators, successors and assigns.

         Any controversy arising out of or relating to this Agreement may be
submitted to and settled by arbitration pursuant to the By-Laws and rules of
the NASD. The Broker-Dealer and the Lender shall be conclusively bound by such
arbitration.

         This instrument embodies the entire agreement between the
Broker-Dealer and Lender and no other evidence of such agreement has been or
will be executed without the prior written consent of the NASD.

         This Agreement shall be deemed to have been made under, and shall be
governed by, the laws of the State of Texas in all respects.

NASD FORM SL-1                         7
<PAGE>   10
IN WITNESS WHEREOF the parties have set their hands and seal this 13th day of
October 1998.

                                        Tejas Securities Group, Inc
                                        ---------------------------------
                                              (Name of Broker-Dealer)

                                        By /s/ JOHN J. GORMAN, IV  L.S.
                                           -----------------------
                                              (Authorized Person)
                                               JOHN J. GORMAN, IV

                                        /s/ CLARK N. WILSON  L.S.
                                        --------------------
                                              (Lender)
                                            Clark N. Wilson

                                        FOR NASD USE ONLY

                                        ACCEPTED BY  /s/ [ILLEGIBLE]
                                                    ---------------------
                                                            (Name)

                                                    Associate Director
                                                    ----------------------
                                                            (Title)

                         *EFFECTIVE DATE:  11/12/98
                         LOAN NUMBER:  06-D-SLA-10095

NASD FORM SL-1

                                       8
<PAGE>   11
                          SUBORDINATED LOAN AGREEMENT
                              LENDER'S ATTESTATION

         It is recommended that you discuss the merits of this investment with
an attorney, accountant or some other person who has knowledge and experience
in financial and business matters prior to executing this Agreement.

                   1.    I have received and reviewed a reprint of Appendix D
                         of 17 CFR 240.15c3-1, and am familiar with its
                         provisions.

                   2.    I am aware that the funds or securities subject to
                         this Agreement are not covered by the Securities
                         Investor Protection Act of 1970.

                   3.    I understand that I will be furnished financial
                         statements pursuant to SEC Rule 17a-5(c).

                   4.    On the date this Agreement was entered into, the
                         broker-dealer carried funds or securities for my
                         account. (State Yes or No) Yes.

                   5.    Lender's business relationship to the broker-dealer
                         is:  client

                   6.    If not a partner or stockholder actively engaged in
                         the business of the broker-dealer, acknowledge receipt
                         of the following:

                         a. Certified audit and accountant's certificate dated
                            12-31-97

                         b. Disclosure of financial and/or operational problems
                            since the last certified audit which required
                            reporting pursuant to SEC Rule 17a-11. (If no such
                            reporting was required, state "none") none

                         c. Balance sheet and statement of ownership equity
                            dated September 30, 1998

                         d. Most recent computation of net capital and aggregate
                            indebtedness or aggregate debit items dated 9-30-97,
                            reflecting a net capital of $1,042,323 and a ratio
                            of 1:1.

                         a. Debt/equity ratio as of 24% of 9-30-98.

                         f. Other disclosures: Possible business combination
                            with EMED

DATED: October 13, 1998              /s/ CLARK N. WILSON           L.S.
                           --------------------------------------
                                          (Lender)
                                       Clark N. Wilson

<PAGE>   12

                              ADDENDUM AGREEMENT

         Reference is hereby made to that certain Subordinated Loan Agreement
dated effective October 13, 1998, between MR. CLARK N. WILSON (the "Lender")
and TEJAS SECURITIES GROUP, INC. (the "Broker-Dealer"), as the same may be
amended or modified from time to time (the "Loan Agreement"). Capitalized terms
used in this Addendum Agreement (the "Addendum"), to the extent not otherwise
defined herein, shall have the same meanings as in the Loan Agreement. The
terms and conditions of the Loan Agreement are incorporated herein by
reference. This Addendum shall constitute additional terms and conditions to
which the Payment Obligation is subject.

         NOW, THEREFORE, IN CONSIDERATION of the premises herein contained and
other good and valuable consideration, the receipt and sufficiency of which are
hereby acknowledged, the Lender and the Broker-Dealer hereby agree as follows:

1. Notwithstanding anything to the contrary set forth in the Loan Agreement,
Broker-Dealer may incur, issue, and permit to exist obligations of the
Broker-Dealer for borrowed money in a principal amount outstanding which shall
not at any time exceed $2,500,000.00, which obligations shall be senior to the
repayment of the Payment Obligation which is the subject of the Loan Agreement.

2. Notwithstanding anything to the contrary set forth in the Loan Agreement,
Broker-Dealer may incur, issue, and permit to exist obligations of
Broker-Dealer for borrowed money in a principal amount outstanding at any time
not to exceed $2,000,000.00, which obligations shall rank pari passu with the
Payment Obligation which is the subject of the Loan Agreement and shall bear
terms substantially similar to the Payment Obligation which is the subject of
the Loan Agreement.

3. Broker-Dealer agrees that, so long as the Payment Obligation or any part
thereof is outstanding, the Broker-Dealer shall not pay salary to its
President, Mr. John Gorman IV, in an amount in excess of $360,000.00 per year.
Broker-Dealer shall however be permitted to provide to Mr. John Gorman IV,
President of Broker-Dealer, in addition to such salary, such additional
standard benefits as Broker-Dealer deems necessary or desirable, including
without limitation stock options, the use of a company automobile, insurance,
and other standard benefits.

4. Broker-Dealer agrees that so long as the Payment Obligation or any part
thereof remains outstanding, Broker-Dealer shall not, without the prior written
consent of the Lender, pay any dividends or make any other payment or
distribution in cash on account of its capital stock.

5. Broker-Dealer agrees that, for so long as the Payment Obligation or any part
thereof remains outstanding, the Broker-Dealer shall authorize a representative
of the Lender to maintain a seat on the Board of Directors of Broker-Dealer.

6. As a condition of the Loan Agreement, Broker-Dealer shall issue to the
Lender, on the date of approval of the transaction which is the subject of the
Loan Agreement by the NASD, warrants to purchase 112,500 shares of common
capital stock of the Broker-Dealer, which warrants shall be exercisable at a
price of $2.65 per share of common stock and shall be exercisable for a period
of five (5) years from the date of issuance of such warrants. The terms

<PAGE>   13
of such warrants, whether or not exercised, shall entitle the Lender to
participate in underwriter warrant distributions on the same basis as
shareholders of the Broker-Dealer at any time while the Payment Obligation or
any part thereof remains outstanding, such distributions to be determined on
the basis that each such warrant for the purchase of a share of common stock
equals a single share of common stock.

7. If Broker-Dealer shall fail to perform, observe, or comply with any
covenant, agreement or term contained in this Addendum, and such failure shall
continue for thirty (30) days after the Lender sends to the Broker-Dealer
notice thereof, such failure shall constitute an Event of Acceleration and
shall entitle the Lender to exercise the rights and remedies available to it
under the Loan Agreement.

8. This Addendum shall be governed by and construed in accordance with the laws
of the State of Texas. THIS ADDENDUM, THE LOAN AGREEMENT, AND THE OTHER
DOCUMENTS REFERRED TO IN THE LOAN AGREEMENT EMBODY THE FINAL, ENTIRE AGREEMENT
AMONG THE PARTIES HERETO AND SUPERSEDE ANY AND ALL PRIOR COMMITMENTS,
AGREEMENTS, REPRESENTATIONS, AND UNDERSTANDINGS, WHETHER WRITTEN OR ORAL,
RELATING TO THE SUBJECT MATTER HEREOF AND MAY NOT BE CONTRADICTED OR VARIED BY
EVIDENCE OF PRIOR, CONTEMPORANEOUS, OR SUBSEQUENT ORAL AGREEMENTS OR
DISCUSSIONS OF THE PARTIES HERETO. THERE ARE NO ORAL AGREEMENTS AMONG THE
PARTIES HERETO. The provisions of this Addendum and the Loan Agreement to which
the Broker-Dealer is a party may be amended or waived only by an instrument in
writing signed by the parties hereto.

9. The unenforceability of any provision of this Addendum shall not affect the
enforceability or validity of any other provision hereof.

10. This Addendum may be executed in any number of counterparts and by
different parties hereto on separate counterparts, each of which when so
executed shall be deemed to be an original and all of which when taken together
shall constitute but one and the same instrument.

11. All notices and other communications provided for in this Addendum shall be
given to the parties hereto at the "Address for Notices" specified below its
name on the signature pages hereof; or as to any party at such other address
as shall be designated by such party in a notice to the other party given in
accordance with this section. All such communications shall be given or made by
telecopy or in writing, mailed by certified mail, return receipt requested, or
delivered to the intended recipient, and shall be deemed to have been duly
given when transmitted by telecopy subject to telephone confirmation of receipt
or when personally delivered, or in the case of a mailed notice, when duly
deposited in the mail, in each case given or addressed as aforesaid.

                                      -2-
<PAGE>   14

                                      Broker-Dealer:

                                      TEJAS SECURITIES GROUP, INC.

                                      By:  /s/ JOHN J. GORMAN, IV
                                          --------------------------------
                                      Name:    John J. Gorman, IV
                                             -----------------------------
                                      Title:   President
                                              ----------------------------

                                      Address for Notices:

                                      1250 Capital of Texas Highway South
                                      ------------------------------------
                                      Building II, Suite 500
                                      ------------------------------------
                                      Austin, Texas 78746
                                      ------------------------------------

                                      Lender:

                                      Mr. Clark N. Wilson
                                      ------------------------------------

                                      By: /s/ CLARK N. WILSON
                                          --------------------------------
                                      Name: Mr. Clark N. Wilson
                                          --------------------------------

                                      Address for Notices:

                                      5312 Park Hollow Lane
                                      ------------------------------------
                                      Austin, Texas 78746
                                      ------------------------------------

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