<PAGE>   1
                                                                   EXHIBIT 10.21

THE INFORMATION BELOW MARKED (*) OR (***) HAS BEEN OMITTED PURSUANT TO A
REQUEST FOR CONFIDENTIAL TREATMENT. THE OMITTED PORTIONS HAVE BEEN SEPARATELY
FILED WITH THE COMMISSION.


                                  AMENDMENT ONE

                                       TO

                                 COVER AGREEMENT

                                     BETWEEN

                  SPRINT COMMUNICATIONS COMPANY L.P. ("SPRINT")
                                       AND
                           WORLDNET, INC. ("CUSTOMER")

This Amendment One ("Amendment") to the Cover Agreement is entered into by and
between Sprint and Customer, effective as of the first day of the next billing
month following execution of this Amendment by both parties.

     WHEREAS, Sprint and Customer entered into a Cover Agreement on September
30, 1996 ("Cover Agreement") for Sprint's provision of ATM and Clearline
products and services (hereinafter referred to as the "Products and Services"),
and

     WHEREAS, Customer wishes to order Sprint's Clarity (Voice) products and
services pursuant to the Sprint Clarity Term Plan Agreement; and

     WHEREAS, the parties wish to amend the Cover Agreement to add the special
prices for the Sprint Clarity Products and Services, and to modify certain
provisions of the Cover Agreement; and

     WHEREAS, Sprint is a telecommunications common carrier providing interstate
and international services to customers: (i) pursuant to tariffs on file with
the Federal Communications Commission (F.C.C.) or in-country international
telecommunications bodies, and, in the case of intrastate services, pursuant to
tariffs on file with the various state regulatory commissions (collectively
referred to as "Tariffs"), as applicable, and as amended from time to time by
Sprint, and (h) on a non-tariff basis.

     NOW THEREFORE, for and in consideration of the mutual agreement and
understandings contained herein, the parties agree as follows.

1.   LOCAL ACCESS FACILITIES

     Sprint agrees to waive installation charges (including non-recurring ACF
     and COC charges) for both Sprint provided and Customer provided Local
     Access Facilities to access the ATM and Clearline Products and Services.
     Accordingly, Section 6(B) of the Agreement is hereby amended by changing
     the first sentence to read as follows (changed text is underlined):

     "Sprint shall waive (*)% of the Sprint installation charges for Sprint or
     Customer provided Local Access Facilities...".

Amendment One to Cover Agreement - WorldNet    1                October 31, 1996
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                         SPRINT PROPRIETARY INFORMATION
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<PAGE>   2
THE INFORMATION BELOW MARKED (*) OR (***) HAS BEEN OMITTED PURSUANT TO A
REQUEST FOR CONFIDENTIAL TREATMENT. THE OMITTED PORTIONS HAVE BEEN SEPARATELY
FILED WITH THE COMMISSION.



2.   SPECIAL PRICES FOR SPRINT CLARITY

     Sprint Clarity Products and Services are provided pursuant to applicable
     tariffs on file with regulatory agencies. Customer shall order Sprint
     Clarity Products and Services by executing a Sprint Clarity Term Plan
     Agreement {"Order")

     A.   Usage Charges

          Beginning on the effective date of this Amendment, Customer shall be
          charged the applicable fixed rates from the table below for its
          interstate Sprint Clarity Outbound Service usage and interstate Sprint
          Clarity Toll Free Service usage, subject to all of the conditions and
          limitations set forth in the Cover Agreement and Sprint F.C.C. Tariff
          No. 12.

<TABLE>
<CAPTION>
          Per Minute Rate (Dedicated)        Per Minute Rate (Switched)
          ---------------------------        --------------------------
          <S>                                <C>
                   $(*)                            $(*)
</TABLE>

     B.   Installation Charges

          Sprint shall waive 100% of the installation charges (including
          non-recurring COC and ACF charges) for Sprint provided T-1 access
          lines used for Sprint domestic voice services provided that such
          access lines are provided for twelve (12) continuous months. If such
          access lines are terminated prior to twelve (12) continuous months,
          then Customer shall be obligated to pay Sprint a pro-rata amount of
          the waived installation charges based on the number of months
          remaining in the minimum required period.

     C.   Other Terms

          1.   During each billing month following the effective date of this
               Amendment and continuing for the Term of the Cover Agreement, a
               minimum of (*) percent (*%) of Customer's Sprint Clarity
               Outbound Service and Sprint Clarity Toll Free Service usage
               minutes must be interstate. If Customer fails to satisfy this
               condition during any two consecutive billing month, then Sprint
               may revise the Sprint Clarity usage charges set forth in this
               Amendment and the Cover Agreement.

          2.   The fourth sentence of Subsection 7.A of the Cover Agreement is
               hereby replaced with the following sentence:

               "The following charges incurred by Customer for the Contributory
               Services (net of all discounts) shall be used in calculating
               Customer's usage toward the Minimum Service Commitment: (a) all
               monthly recurring charges for the ATM Products and Services; (b)
               the monthly circuit charges for the interexchange portion for the
               Clearline Products and Services; and (c) Sprint Clarity Service
               usage charges."

          3.   Subsection 8.A.2 and Attachment B of the Cover Agreement shall
               not apply to Sprint Clarity Products and Services.

3.   ENTIRE AGREEMENT

     A.   This Amendment One represents the entire agreement between the parties
          with respect to the subject matter hereof and supersedes all prior
          statements, communications or agreements, whether oral or written,
          between the parties.

Amendment One to Cover Agreement - WorldNet          2          October 31, 1996
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                         SPRINT PROPRIETARY INFORMATION
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<PAGE>   3


     B.   This Amendment One, the Cover Agreement, the Orders and all applicable
          Tariffs shall represent the entire agreement between the parties with
          respect to Sprint's provision of the Products and Services. In the
          event of any conflict between any of the aforementioned documents, the
          following shall be the order of precedence: (1) the applicable
          Tariffs, (2) this Amendment One, (3) the Cover Agreement, and (4) the
          Orders.

IN WITNESS WHEREOF, the parties hereto have caused this Amendment One to the
Agreement to be executed by their duly authorized representatives.

WORLDNET, INC.                               SPRINT COMMUNICATIONS COMPANY, L.P.

By:                                          By:


 /s/ DAN E. STROUD                            /s/ TIM HAMMONDS
--------------------------------             --------------------------------
Signature                                    Signature


 DAN E. Stroud                                Tim Hammonds
--------------------------------             --------------------------------
Name Typed or Printed                        Name Typed or Printed


 V.P. Network Operations                      Branch Manager
--------------------------------             --------------------------------
Title                                        Title


 11/6/96                                      11/7/96
--------------------------------             --------------------------------
Date                                         Date


Amendment One to Cover Agreement - WorldNet          3          October 31, 1996
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                         SPRINT PROPRIETARY INFORMATION
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