Exhibit 99.100


Milan, 15th November 2007


To:
Telefonica S.A.
Gran Via no. 38, Planta 9
Madrid, Spain
ATTENTION: GROUP GENERAL COUNSEL - RAMIRO SANCHEZ DE LERIN-OVIES

Telco S.p.A.
Galleria del Corso no. 2
20122 Milan, Italy
ATTENTION: CHAIRMAN OF THE BOARD OF DIRECTORS

                                                            PERSONALLY DELIVERED

                   RE: ADHERENCE TO THE CALL OPTION AGREEMENT

Dear Sirs,

We make  reference  to the  agreement  executed  on 6th  November  2007  between
Telefonica S.A. and Telco S.p.A. according to which Telefonica S.A. has received
the right to purchase from Telco S.p.A.  and/or Olimpia S.p.A.,  as the case may
be, the shares of Olimpia S.p.A.  or Telecom Italia S.p.A.  subject to the terms
and conditions provided therein (the "CALL OPTION AGREEMENT").

According to the relevant  provisions of Article 5 of the Call Option Agreement,
the  undersigned  company  Olimpia S.p.A.  hereby adheres to and accepts all the
terms and conditions of the Call Option Agreement.

Kind regards,

Olimpia S.p.A.

By: _______________
Title: Director



For acceptance

Telefonica S.A.                                      Telco S.p.A.

By: ______________                                          By:   ______________

Title: Special Attorney                                     Title: Chairman