<PAGE>
                                                                    Exhibit 10.3


  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.

          15TH INSTRUMENT OF ADDENDUM TO AGREEMENT N(0)VES-8-IDN-1-1999

                           ENTERED INTO ON 10/18/1999.


AOL BRASIL LTDA, with its headquarters at Avenida Industrial, 600, 2(0) andar,
CEP 08090-500, in the city of Sao Paulo, State of Sao Paulo, enrolled in the
National Registry of Legal Entities [CNPJ/MF] under n(0) 03.032.579/0001-62,
hereby represented pursuant to its Articles of Association, hereinafter called
"AOL", and

EMPRESA BRASILEIRA DE TELECOMUNICACOES S.A. - EMBRATEL, with its headquarters at
Avenida Presidente Vargas, 1012, CEP 20179-900, in the city of Rio de Janeiro,
State of Rio de Janeiro, enrolled in the National Registry of Legal Entities
[CNPJ/MF] under n(0) 33.530.486/0001-29, hereby represented pursuant to its
Articles of Association, hereinafter called "EMBRATEL", both corporations also
jointly called PARTIES and, individually, PARTY;

WHEREAS:

     a. the Parties, on 10/18/1999 entered into the Agreement "Master Agreement
     for Value Added Services (BRAZIL)", hereinafter called AGREEMENT;

     b. the AGREEMENT has been the object of addendums, Ad. 001/00, Ad. 002/00,
     Ad. 003/00, Ad. 004/01, Ad. 005/01, Ad. 006/01, Ad. 007/01, Ad. 008/01, Ad.
     009/01, Ad. 010/02, Ad.011/01, Ad. 012/02 and Ad.013/03, Ad. 014/03
     respectively signed on 05/10/00, 09/29/00, 12/27/00, 04/25/01, 07/04/01,
     07/31/01, 09/21/01, 11/01/01, 12/03/01, 04/03/01, 05/25/02 and 11/01/02,
     09/03/03;

     c. the Parties intend to change some of the AGREEMENT's terms and
     conditions, particularly excluding the supply of certain Dedicated Modems,

they decide to sign the present 15th Addendum to the AGREEMENT (hereinafter
simply called ADDENDUM), under the following terms and pointing out that the
expressions written in capital letters bear the same definition and meaning set
forth in the AGREEMENT.

FIRST CLAUSE: THE AIM

The present ADDENDUM aims at the IMMEDIATE deactivation of [**] ([**]) modems
("Dedicated Modems"), as set forth in the list below:


                  City                            Modems
                  ----                            ------

                  [**]                               [**]
                  [**]                               [**]
                  [**]                               [**]
                  [**]                               [**]




<PAGE>

                  [**]                               [**]
                  [**]                               [**]
                  [**]                               [**]
                  [**]                               [**]
                  [**]                               [**]
                  [**]                               [**]
                  [**]                               [**]
                  [**]                               [**]
                  [**]                               [**]
                  [**]                               [**]
                  [**]                               [**]
                  [**]                               [**]
                  [**]                               [**]
                  [**]                               [**]
                  [**]                               [**]
                  [**]                               [**]
                  [**]                               [**]
                  [**]                               [**]
                  TOTAL                              [**]

SECOND CLAUSE - MISCELLANEOUS

2.1. The Parties ratify the other provisions of the AGREEMENT, which shall be
fully kept in whatever they do not conflict with the present ADDENDUM.

2.2. The present ADDENDUM binds the Parties per se, their successors, heirs and
assignees at any title.

In witness whereof, the Parties sign the present ADDENDUM in two (02)
counterparties of equal form and content in the presence of two (02) undersigned
witnesses.


Rio de Janeiro , September 25, 2003.



EMPRESA BRASILEIRA DE TELECOMUNICACOES S.A.


/S/MICHELE DARIANO MACHEMER                /S/ DEBORA FERREIRA SELLAN
-------------------------------------      -------------------------------------
BY:  MICHELE DARIANO MACHEMER              BY:  DEBORA FERREIRA SELLAN
POSITION:  Manager Sales                   POSITION:  Manager Account



AOL BRASIL LTDA


/S/ MILTON DA ROCHA CAMARGO
-------------------------------------
BY: MILTON DA ROCHA CAMARGO
POSITION:  PRESIDENT





                                       2
<PAGE>

WITNESSES:


/S/ CARLOS TRINDADE BORGONOVI              /S/ GISELE BRAZ
-------------------------------------      -------------------------------------
BY:  CARLOS TRINDADE BORGONOVI             BY:  GISELE BRAZ








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