Exhibit 8.1

Significant Subsidiaries and Affiliates

The following table sets forth our
significant subsidiaries and our affiliate accounted for using the equity method at December 31, 2011:



|                                                    |  |                              |  |                                          |  |                                                                                                                                                                                                                                                                                                                                
|--------------------------------------------------- |  | ---------------------------- |  | ---------------------------------------- |  | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|Name of Company                                     |  | Jurisdiction ofestablishment |  | Percentage ofownershipand votinginterest |  | Description                                                                                                                                                                                                                                                                                                                    
|Subsidiaries                                        |  |                              |  |                                          |  |                                                                                                                                                                                                                                                                                                                                
|Integración de Servicios TMX, S.A. de C.V.          |  | Mexico                       |  | 100%                                     |  | Intermediate holding company.                                                                                                                                                                                                                                                                                                  
|Alquiladora de Casas, S.A. de C.V.                  |  | Mexico                       |  | 100%                                     |  | Real estate company owning our facilities.                                                                                                                                                                                                                                                                                     
|Compañía de Teléfonos y Bienes Raíces, S.A. de C.V. |  | Mexico                       |  | 100%                                     |  | Real estate company owning our facilities.                                                                                                                                                                                                                                                                                     
|Consorcio Red Uno, S.A. de C.V.                     |  | Mexico                       |  | 100%                                     |  | Supplier of telecommunications network integration services and information systems.                                                                                                                                                                                                                                           
|Teléfonos del Noroeste, S.A. de C.V.                |  | Mexico                       |  | 100%                                     |  | Fixed-line public network concessionaire for the state of Baja California Norte and the San Luis Rio Colorado region of the state of Sonora.                                                                                                                                                                                   
|Uninet, S.A. de C.V.                                |  | Mexico                       |  | 100%                                     |  | Provider of corporate networks and Internet access services to Telmex and corporate customers.                                                                                                                                                                                                                                 
|Telmex USA, L.L.C.                                  |  | Delaware(United States)      |  | 100%                                     |  | Authorized long-distance service re-seller and provider of payment collection services for lines in Mexico (installation and monthly rental), and authorized by the United States
Federal Communications Commission to provide facility-based long-distance services, data transmission and cross-border data transit services.
|                                                    |  |                              | 
|Affiliated company                                  |  |                              |  |                                          |  |                                                                                                                                                                                                                                                                                                                                
|Grupo Telvista, S.A. de C.V.                        |  | Mexico                       |  | 45%                                      |  | Provider of telemarketing services in the United States and Mexico.