America Movil, the largest cellphone operator in Latin America, posted a 51 percent rise in third-quarter net profit on Monday due to a pickup in new subscribers and lower financing costs.

America Movil , controlled by billionaire Carlos Slim, said it earned 18.681 billion pesos ($1.38 billion) in the July-September period.

The company signed up 4.0 million new clients in the third quarter, slightly fewer than forecast in a Reuters poll of analysts.

Quarterly revenue rose 17 percent, year over year, to 99.762 billion pesos, driven by strong growth in Internet and other third-generation services, America Movil said in a statement.

Earnings before interest, taxes, depreciation and amortization totaled 40.4 billion pesos, up 16 percent from the same quarter in 2008 and slightly beating forecasts.

America Movil is betting heavily on Internet-oriented products, promoting smartphones and selling cheap laptop computers and modems on monthly payment plans.

It said sales from data services such as text messages and Internet grew an average of 58 percent in its various markets during the quarter.

Data continued to be the major driver of revenue growth as the 3G services that for the most part our subsidiaries started offering last year met strong demand from our clients, America Movil said.

Financing costs fell 83 percent year over year to 653 million pesos, helped by movements in several currencies.

The company, which has operations from the United States to Argentina and competes regionally with Spain's Telefonica SA , ended September with 198 million clients.

Client growth was led by Brazil, with 1.8 million net additions, followed by America Movil's Tracfone operator in the United States, with 712,000. Mexico added 280,000 net new clients.

Client additions were stronger in the third quarter than in the April-June period, but still far below the 7.3 million net new subscribers picked up in the third quarter of last year.

America Movil shares rose 1.22 percent to 30.69 pesos ahead of the earnings report.

Latin Americans in well-heeled neighborhoods such as Sao Paulo's Jardins and Mexico City's Polanco are increasingly surfing the Internet on Research in Motion Ltd's BlackBerries and Apple Inc's iPhones. But most people in the region continue to use much less expensive handsets on pay-as-you-go plans.

($1=13.5035 pesos at end-Sept)

(Reporting by Noel Randewich, editing by Leslie Gevirtz, Matthew Lewis and Andre Grenon)

Argentina