Billionaire Carlos Slim's America Movil, one of the world's biggest telecommunications firms, sees growth in new mobile subscribers slowing by around a third in 2011 due to the saturation of Latin America's markets.

After posting sizzling growth in its customer base through the last decade, America Movil is facing slower expansion ahead as most Latin Americans now have mobile phones.

Penetrations are high in some countries, said Chief Executive Officer Daniel Hajj in a conference call with analysts.

We think in wireless around 16 to 17 million wireless subscribers is what we think we could do this year, he said, adding that the company saw around 5 million new fixed-line, broadband and TV subscribers during the year.

The company added 24.1 million wireless subscribers in 2010 and beat expectations for new clients during the fourth quarter in results posted on Tuesday, with 8.2 million new subscribers, mostly in Brazil and Mexico.

U.S.-traded shares in America Movil shed 2.18 percent to $56.09 while its Mexican-traded shares fell 1.88 percent to 33.89 pesos.

(Reporting by Michael O'Boyle and Tomas Sarmiento, editing by Dave Zimmerman)