Document:

<PAGE>
                                                                   Exhibit 10.51

(21 EMBRATEL LOGO)         AMENDMENT NUMBER 12/2002 TO CONTRACT VES-8-IDN-1-1999
--------------------------------------------------------------------------------

Portions of this Exhibit were omitted and have been filed separately with the
Secretary of the Commission pursuant to the Company's application requesting
confidential treatment under Rule 24b-2 of the Securities Exchange Act.

                                               AMENDMENT #12 TO MASTER AGREEMENT

                                FOR VALUE ADDED SERVICES (BRAZIL) BY AND BETWEEN
     AOL BRASIL LTDA. AND EMPRESA BRASILEIRA DE TELECOMUNICAcoES S.A. - EMBRATEL

         This twelfth amendment (the "Amendment # 12") to the Master Agreement
for Value Added Services (Brazil) dated October 18, 1999 (the "Agreement") is
made and entered into as of November 01, 2002 ("Amendment Date"), by and between
AOL BRASIL LTDA., a Brazilian corporation headquartered at Avenida Industrial
600, 2(degree). Andar, Santo Andre, 08090-500, Sao Paulo - SP, registered with
the Ministerio de Fazenda under number 03.032.579/0001-62, hereinafter called
AOL, and EMPRESA BRASILEIRA DE TELECOMUNICACOES S.A. - EMBRATEL, a Brazilian
corporation headquartered at Av. Presidente Vargas, 1.012, 20179-900, Rio de
Janeiro - RJ, registered with the Ministerio de Fazenda under number
33.530.486/0001-29, hereinafter called EMBRATEL.

         Unless modified herein, all other terms defined in the Agreement shall
have the same meaning when used in this Amendment.

         All terms and conditions of the Agreement not otherwise specifically
modified in this Amendment remain unchanged and in full force and effect.

         In the case of conflict between any provision of this Amendment #12 and
any provision of the Agreement not expressly modified herein, this Amendment #12
shall control.

The Parties, in consideration of the mutual covenants herein expressed, agree
with each other as follows:

         1. THE OBJECT

         1.1 Pursuant to this Amendment #12, Section 2.6(c) ("International
Transit Fees") of the Agreement - as modified by its amendments #1 and #8 - is
completely deleted and hereby replaced by a new Section 2.6 (c) as follows:

                  " (c) [**] per month to the STM-1 capacity on the Americas II
                  Circuit.

                  The prices presented above do not include any taxes.

                  The International Transit Fees are for an international
                  circuit from AOL in Virginia - USA, terminating in one of

                              HIGHLY CONFIDENTIAL

                                       1
<PAGE>
(21 EMBRATEL LOGO)         AMENDMENT NUMBER 08/2001 TO CONTRACT VES-8-IDN-1-1999
--------------------------------------------------------------------------------

                  EMBRATEL's operations buildings in Sao Paulo - Brazil. Any
                  changes to the circuit termination outside of EMBRATEL's
                  facilities in the city of Sao Paulo may require price
                  adjustment."

         1.2 The provisions set forth in Clause 5 of Amendment #012000, dated
May 10, 2000, or any other [**] provision included in the Agreement, shall not
apply to the price expressed in section 2.6(c) of the Agreement, as amended
above, for a period of two (2) years initiating on the date in which this
Amendment is executed.

IN WITNESS WHEREOF, the parties hereto have executed this Amendment effective as
of the Amendment Date.

                                                 Sao Paulo,   November  01, 2002

EMPRESA BRAS. TELECOMUNICACOES S/A              AOL BRASIL LTDA.
            - EMBRATEL

By:                                          By:
    /s/ Valdinei Carniel Rocha                       /s/ Milton Camargo
-----------------------------------------    -----------------------------------
        Valdinei Carniel Rocha                           Milton Camargo
       EXECUTIVE ACCOUNT MANAGER                        VICE- PRESIDENT

By:  /s/ Michele Dariano Machemer
-----------------------------------------
         Michele Dariano Machemer
            ACCOUNT MANAGER

WITNESSES:

By:  ____________________________________    By:  ______________________________

                              HIGHLY CONFIDENTIAL

                                       2<PAGE>
                                                                  Exhibit 10.54

Portions of this Exhibit were omitted and have been filed separately with the
Secretary of the Commission pursuant to the Company's application requesting
confidential treatment under Rule 24b-2 of the Securities Exchange Act.

AGREEMENT ENTERED INTO BY AND BETWEEN AVANTEL, S.A., HEREIN REPRESENTED BY MR.
FERNANDO BELLIDO CASTANOS, ACTING AS THE LEGAL REPRESENTATIVE, HEREINAFTER
REFERRED TO AS "AVANTEL", AND AOL MEXICO, S. DE R.L. DE C.V. HEREIN REPRESENTED
BY LIC. FERNANDO ZETINA ARBESU, ACTING AS LEGAL REPRESENTATIVE, HEREINAFTER
REFERRED TO AS "AOL"; BOTH AVANTEL AND AOL MAY JOINTLY BE REFERRED TO AS THE
"PARTIES", UNDER THE FOLLOWING BACKGROUND, REPRESENTATIONS AND ARTICLES.

                                   BACKGROUND

I.- On January 20, 2000, the PARTIES entered into a Master Agreement for Data
Communications and Value Added Services, under which AVANTEL provides AOL Port
installation, activation, maintenance and operation services ("Modems or Ports")
for AOL Switched Access National Network, as provided in Section 1 of the
Agreement and according to Exhibits "D" and "C" thereof. On October 31, 2001,
the PARTIES entered into a Letter Agreement to amend certain terms of the
Agreement ("Letter Agreement"). The Agreement and its Exhibits, together with
the new and amended terms set forth in Letter Agreement, shall be hereinafter
referred to as the "MAIN AGREEMENT".

II.- On October 31, 2001, the PARTIES entered into an ADDENDUM applicable only
for the rates of the [**] Ports delivered through the [**] E1's AOL requested
directly to the Local Service Provider, as provided in Section 1.1.(a) of the
MAIN AGREEMENT, modifying Section 2 of the MAIN AGREEMENT only regarding the
rates of such [**] Ports.

                          R E P R E S E N T A T I O N S

I.- PARTIES hereto acknowledge that this Agreement shall only be applicable for
the [**] Ports that are being cancelled according to what has been already
negotiated and agreed by the PARTIES and which Ports are identified in Annex 1
attached hereto. All the other terms and conditions of the MAIN AGREEMENT and
the ADDENDUM, shall remain in full force and effect for the remaining Ports,
which are identified in Annex 2.

II.- PARTIES hereto acknowledge the personality and faculties they claim,
acknowledging that such faculties have not been revoked, modified or limited any
way, and therefore they may bind themselves under the terms of this Agreement.

III.- This Agreement, signed by the parties, is made part of the MAIN AGREEMENT.

IV.- PARTIES hereto agree to execute this Agreement under the terms and
conditions set forth herein below:

                                     CLAUSES

FIRST.-  PURPOSE.
PARTIES agree to execute this Agreement in order to cancel the [**] Ports
identified in Annex 1 attached hereto as of the effective date specified in
Annex 1, as established in the Background and the Representations of this
Agreement, and as provided in the MAIN AGREEMENT and ADDENDUM.

                                       4
<PAGE>

Therefore, AOL has paid the penalties for the early cancellation of the [**}
Ports which are detailed in the invoices AVANTEL sent to AOL, and is willing to
pay upon the execution of this Agreement, the outstanding debts detailed in the
following table:

<TABLE>
<CAPTION>

------------------------------------------------------------   --------------------------------------
                      INVOICES IN MXP                                     PAYMENTS IN MXP
------------------------------------------------------------   --------------------------------------
Invoice        Subtotal           Tax      Subtotal plus       Invoice      Payment    Payment Amount    Payment
   Date                                         Tax            Number         Date                        Status
---------------------------------------------------------------------------------------------------------------------
<S>            <C>              <C>            <C>             <C>          <C>           <C>              <C>
  21/02/02     $ [**]           $ [**]         $ [**]           A41507      11/07/02      $ [**]           [**]
---------------------------------------------------------------------------------------------------------------------
  28/03/02     $ [**]           $ [**]         $ [**]           A42906      11/07/02      $ [**]           [**]
---------------------------------------------------------------------------------------------------------------------
  28/03/02     $ [**]           $ [**]         $ [**]           A42905      11/07/02      $ [**]           [**]
---------------------------------------------------------------------------------------------------------------------
  22/05/02     $ [**]           $ [**]         $ [**]           A44949                                     [**]
---------------------------------------------------------------------------------------------------------------------

               ======================================================================================================
               $ [**]           $ [**]         $ [**]                                     $ [**]
</TABLE>

<TABLE>
<CAPTION>

------------------------------------------------------------    --------------------------------------
                      INVOICES IN USD                                  PAYMENTS IN USD
------------------------------------------------------------    --------------------------------------
Invoice        Subtotal           Tax      Subtotal plus        Invoice      Payment    Payment Amount  Payment Status
   Date                                          Tax            Number        Date
----------------------------------------------------------------------------------------------------------------
<S>            <C>              <C>            <C>             <C>          <C>           <C>              <C>
  21/02/02     $ [**]            $ [**]         $ [**]           A41371      11/07/02      $ [**]           [**]
----------------------------------------------------------------------------------------------------------------
  26/02/02     $ [**]            $ [**]         $ [**]           A41509      11/07/02      $ [**]           [**]
----------------------------------------------------------------------------------------------------------------
  27/03/02     $ [**]            $ [**]         $ [**]           A46404      11/07/02      $ [**]           [**]
----------------------------------------------------------------------------------------------------------------
  27/03/02     $ [**]            $ [**]         $ [**]           A46402      11/07/02      $ [**]           [**]
----------------------------------------------------------------------------------------------------------------
  13/03/02     $ [**]            $ [**]         $ [**]           A42135                                     [**]
----------------------------------------------------------------------------------------------------------------
  27/03/02     $ [**]            $ [**]         $ [**]           A46405                                     [**]
----------------------------------------------------------------------------------------------------------------
  27/03/02     $ [**]            $ [**]         $ [**]           A46403                                     [**]
----------------------------------------------------------------------------------------------------------------
  28/03/02     $ [**]            $ [**]         $ [**]           A42908                                     [**]
----------------------------------------------------------------------------------------------------------------
  22/05/02     $ [**]            $ [**]         $ [**]           A44950                                     [**]
----------------------------------------------------------------------------------------------------------------
               $ [**]            $ [**]         $ [**]           A47930                                     [**]
----------------------------------------------------------------------------------------------------------------

          ======================================================================================================
              $ [**]             $ [**]         $ [**]                                     $ [**]
</TABLE>

AVANTEL recognizes and acknowledges having received at its entire satisfaction
the payments referred to in the previous table and expressly states that the
amounts of these payments were calculated by AVANTEL itself and accepted by AOL.

Therefore, with the signature of this Agreement, AVANTEL receives this moment at
its entire satisfaction the payments made by AOL in the amounts of: $[**]
Mexican Pesos, Value Added Tax Included, wire transfer to [**], Account No. [**]
in favour of AVANTEL, S.A. and $[**] United States Dollars, Value Added Tax
Included, wire transfer to the [**], Account No. [**] ABA [**] in favour of
AVANTEL S.A:, against Invoices Nos. A44949, A42135, A46405, A46403, A42908,
A44950 and A47930 all of them issued by AVANTEL and already in possesion of AOL,
with this, the invoices are terminated; any debit that AOL had with AVANTEL
regarding the port connections identified in Annex 1 attached hereto.

As a consecuence of the payments AVANTEL had previously received and the
payments AVANTEL is receiveing in this moment, AVANTEL acknowledges and
understands that these amounts represent the only payments AVANTEL is entitled
to charge to AOL in connection with the cancellation of the Ports.

SECOND.  RELEASE.
As consequence of having received at its entire satisfaction and conformity the
payment of the amounts referred to in the first article, upon execution of this
Agreement, AVANTEL on behalf of itself and all of its officers, directors,
stockholders, employees, agents, successors, assigns, parent and subsidiary
corporations, and related

                                       2
<PAGE>

entities and affiliates (collectively, the "AVANTEL Releasing Parties"), hereby
releases and irrevocably discharges AOL and all of AOL's officers, directors,
stockholders, employees, agents, successors, assigns, parent and subsidiary
corporations, and related entities and affiliates (collectively, the "AOL
Released Parties") from any and all complaints, claims, causes of action, suits,
costs, losses, liabilities, damages, and demands of any kind, whether known or
unknown (collectively, "Claims"), which any of the AVANTEL Releasing Parties has
alleged or could have alleged against any of the AOL Released Parties as of the
Effective Date, which relate to, or arise from the subject matter of the MAIN
AGREEMENT.

THIRD.-  GENERAL
Parties hereto acknowledge that this Agreement shall only be applicable for the
[**] Ports that are being cancelled according to the First clause of this
document; consequently, all the other terms and conditions of the MAIN AGREEMENT
and the ADDENDUM, shall remain in full force and effect for the remaining Ports,
which are identified in Annex 2.

FOURTH.- CONFIDENTIALITY
This Agreement, including the amounts paid by AOL to AVANTEL hereunder, shall be
considered as confidential by the PARTIES, and shall be governed as stated in
Section 9 of the MAIN AGREEMENT.

FIFTH.- LANGUAGE
This Agreement may be executed in Spanish and English, provided however that the
Spanish version shall always prevail in the event of any disputes concerning
this Agreement.

SIXTH.-  JURISDICTION, INTERPRETATION AND ENFORCEABILITY.
For the interpretation, fulfillment and enforceability of this document, PARTIES
submit themselves to the applicable laws and competent federal courts in Mexico
City, Federal District, expressly waving any other forum to which they could be
entitled resulting from their present or future domiciles.

Considering this Agreement contains no article contrary to law, and contains no
willful act, bad intention or any other reason that may invalidate it, PARTIES
sign two copies on December 13th, 2002, and such date shall be the day on which
this Agreement becomes effective ("Effective Date").

          AVANTEL, S.A.                     AOL MEXICO, S. DE R.L. DE C.V.

  /s/ FERNANDO BELLIDO CASTANOS               /s/ FERNANDO ZETINA ARBESU
--------------------------------           -------------------------------
   MR. FERNANDO BELLIDO CASTANOS             LIC. FERNANDO ZETINA ARBESU

                                       3
<PAGE>

                            ANNEX 1 TO THE AGREEMENT

<TABLE>
<CAPTION>

<S>       <C>           <C>       <C>         <C>         <C>        <C>           <C>         <C>      <C>
 City     1st Canc.     City     2nd Canc.       City     3rd Canc.      City     4th Canc.     City    5th Canc.
Cancun       [**]      Morelia      [**]      Coatzacoalcos [**]     Cd. Obregon     [**]     Chihuahua   [**]
                                    [**]      San Andres    [**]                     [**]                 [**]
Culiacan     [**]      Villahermosa           Tuxtla                 Oaxaca                   Tlaxcala
Mazatlan     [**]      SLP          [**]      Cd. del Carmen[**]     Nuevo Laredo    [**]     Tulancingo  [**]
Cuautla      [**]      Mazatlan     [**]      Campeche      [**]     Villahermosa    [**]     Tula        [**]
Texcoco      [**]      Ocotlan      [**]      Villahermosa  [**]     Mexicali        [**]     Tijuana     [**]
Tepatitlan   [**]      Tepatitlan   [**]      Cancun        [**]     Puerto Vallarta [**]     Cuernavaca  [**]
Toluca       [**]      Mexico, D.F. [**]      Texcoco       [**]     Hermosillo      [**]     Leon        [**]
Mexico, D.F. [**]      Merida       [**]      Cordoba       [**]     Tepic           [**]
SLP          [**]      Tijuana      [**]      Celaya        [**]     Culiacan        [**]
Toluca       [**]      Mexico, D.F. [**]      Orizaba       [**]     Mazatlan        [**]
Veracruz     [**]      Torreon      [**]      Queretaro     [**]     Durango         [**]
Mexico, D.F. [**]      Jalapa       [**]      Toluca        [**]     Chihuahua       [**]
Monterrey    [**]      Ags.         [**]      Irapuato      [**]     Tepatitlan      [**]
Leon         [**]      CD. Valles   [**]      Monterrey     [**]     Merida          [**]
Jalapa       [**]      CD. Valles   [**]      Guanajuato    [**]     CD. Victoria    [**]
Merida       [**]      Orizaba      [**]      Merida        [**]     Mexico, D.F.    [**]
CD. Valles   [**]      Irapuato     [**]      Mexico, D.F.  [**]     Poza Rica       [**]
CD. Valles   [**]      Tlaxcala     [**]      Matamoros     [**]     Torreon         [**]
Orizaba      [**]      Texcoco      [**]      Jalapa        [**]     Merida          [**]
Irapuato     [**]      Tehuacan     [**]      Guadalajara   [**]     Ags.            [**]
Tehuacan     [**]      Cordoba      [**]      Veracruz      [**]     Orizaba         [**]
Cordoba      [**]      CD. Victoria [**]      Queretaro     [**]     Tlaxcala        [**]
CD. Victoria [**]      Celaya       [**]      Saltillo      [**]     Tehuacan        [**]
Celaya       [**]      Zacatecas    [**]      Ags.          [**]     Celaya          [**]
Tulancingo   [**]      Tulancingo   [**]      SLP           [**]     Pachuca         [**]
Tula         [**]      Tula         [**]      Torreon       [**]     Cuautla         [**]
Poza Rica    [**]      Poza Rica    [**]      Reynosa       [**]     Mexico, D.F.    [**]
Pachuca      [**]      Pachuca      [**]      Tampico       [**]     Veracruz        [**]
Cuautla      [**]      Merida       [**]      Cuernavaca    [**]     Puebla          [**]
Guadalajara  [**]      Tijuana      [**]      Tijuana       [**]     Torreon         [**]
CD. Juarez   [**]      Guadalajara  [**]      Leon          [**]     Guadalajara     [**]
Chihuahua    [**]      Guadalajara  [**]      CD. Juarez    [**]     Toluca          [**]
Tampico      [**]                             Puebla        [**]
Guadalajara  [**]                             Chihuahua     [**]
Veracruz     [**]                             Toluca        [**]
Cuernavaca   [**]                             Cuernavaca    [**]
Guadalajara  [**]                             Puebla        [**]
CD. Juarez   [**]                             Monterrey     [**]
Monterrey    [**]                             Guadalajara   [**]
Queretaro    [**]                             Toluca        [**]
Monterrey    [**]                             MEXICO, D.F.  [**]
Guadalajara  [**]
Mexico, D.F. [**]
Mexico, D.F. [**]
Mexico, D.F. [**]
Cuernavaca   [**]
Puebla       [**]
Queretaro    [**]
Monterrey    [**]
Guadalajara  [**]
Puebla       [**]

--------------------   -----------------      ------------------     --------------------     ----------------
  TOTAL OF               TOTAL OF              TOTAL OF                 TOTAL OF                TOTAL OF
  CANCELLED              CANCELLED             CANCELLED                CANCELLED               CANCELLED
    PORTS    [**]          PORTS    [**]       PORTS       [**]         PORTS       [**]        PORTS     [**]
====================   =================      ==================     ====================     ================

 EFFECTIVE DATE OF      EFFECTIVE DATE OF      EFFECTIVE DATE OF       EFFECTIVE DATE OF      EFFECTIVE DATE OF
   CANCELLATION           CANCELLATION           CANCELLATION            CANCELLATION           CANCELLATION
    FEB/01/2002            APR/01/2002            MAY/01/2002             JUNE/01/2002           JULY/01/2002
</TABLE>

                                       4
<PAGE>

                            ANNEX 2 TO THE AGREEMENT
<TABLE>
<CAPTION>

<S>                 <C>                             <C>           <C>
     CIUDAD          Puertos 3COM                     CIUDAD       Puertos VISP
----------------------------------------            -----------------------------------
Aguascalientes        [**]                          Cd. Juarez       [**]
----------------------------------------            -----------------------------------
Cd. Juarez            [**]                          Chihuahua        [**]
----------------------------------------            -----------------------------------
Cd. Victoria          [**]                          Tampico          [**]
----------------------------------------            -----------------------------------
Celaya                [**]                          Celaya           [**]
----------------------------------------            -----------------------------------
Chihuahua             [**]                          Cd. Valles       [**]
----------------------------------------            -----------------------------------
Cordoba               [**]                          Cd. Victoria     [**]
----------------------------------------            -----------------------------------
Cuautla               [**]                          Cordoba          [**]
----------------------------------------            -----------------------------------
Cuernavaca            [**]                          Cuautla          [**]
----------------------------------------            -----------------------------------
Gan                   [**]                          Irapuato         [**]
----------------------------------------            -----------------------------------
Guadalajara           [**]                          Orizaba          [**]
----------------------------------------            -----------------------------------
Guadalajara           [**]                          Pachuca          [**]
----------------------------------------            -----------------------------------
Guanajuato            [**]                          Poza Rica        [**]
----------------------------------------            -----------------------------------
Irapuato              [**]                          Tehuacan         [**]
----------------------------------------            -----------------------------------
Jalapa                [**]                          Tepatitlan       [**]
----------------------------------------            -----------------------------------
Leon                  [**]                          Texcoco          [**]
----------------------------------------            -----------------------------------
Matamoros             [**]                          Tlaxcala         [**]
----------------------------------------            -----------------------------------
Merida                [**]                          Tula             [**]
----------------------------------------            -----------------------------------
Mexico                [**]                          Tulancingo       [**]
----------------------------------------            -----------------------------------
Monterrey             [**]                          Zacatecas        [**]
----------------------------------------            -----------------------------------
Monterrey             [**]                          Aguascalientes   [**]
----------------------------------------            -----------------------------------
Orizaba               [**]                          Jalapa           [**]
----------------------------------------            -----------------------------------
Pachuca               [**]                          Leon             [**]
----------------------------------------            -----------------------------------
Poza Rica             [**]                          Torreon          [**]
----------------------------------------            -----------------------------------
Puebla                [**]                          Merida           [**]
----------------------------------------            -----------------------------------
Queretaro             [**]                          Veracruz         [**]
----------------------------------------            -----------------------------------
Reynosa               [**]                          Ocotlan          [**]
----------------------------------------            -----------------------------------
Saltillo              [**]                          Cd.Obregon       [**]
----------------------------------------            -----------------------------------
San Luis Potosi       [**]                          Culiacan         [**]
----------------------------------------            -----------------------------------
Tampico               [**]                          Durango          [**]
----------------------------------------            -----------------------------------
Texcoco               [**]                          Hermosillo       [**]
----------------------------------------            -----------------------------------
Tijuana               [**]                          Mazatlan         [**]
----------------------------------------            -----------------------------------
Toluca                [**]                          Mexicali         [**]
----------------------------------------            -----------------------------------
Torre Esmeralda       [**]                          Morelia          [**]
----------------------------------------            -----------------------------------
Torreon               [**]                          NuevoLaredo      [**]
----------------------------------------            -----------------------------------
Veracruz              [**]                          Oaxaca           [**]
----------------------------------------            -----------------------------------
Zacatecas             [**]                          PuertoVallarta   [**]
----------------------------------------            -----------------------------------
Cancun                [**]                          Tepic            [**]
----------------------------------------            -----------------------------------
Villahermosa          [**]                          Tuxtla Gutierrez [**]
----------------------------------------            -----------------------------------
Campeche              [**]                          Acapulco         [**]
----------------------------------------            -----------------------------------
San Andres Tuxtla     [**]
----------------------------------------
Coatzacoalcos         [**]                                           [**]
----------------------------------------
Cd. Del Carmen        [**]
----------------------------------------
                         [**]
---------------------
TOTAL PUERTOS                [**]
---------------------
(3COM Y MAX TNT)
</TABLE>

                                       5

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