* Forex gains propel bottom line
* Wireless clients total 256 mln from U.S. to Argentina
* Quarterly revenue rose 4.5 pct from yr ago
MEXICO CITY, Oct 25 (Reuters) - America Movil, the biggest cellphone company in Latin America, posted a 67 percent jump in third-quarter net profit helped by an unusually strong foreign exchange gain as it added results from new operations in Europe.
The company, owned by Mexican tycoon Carlos Slim, earned 30.587 billion pesos ($2.4 billion) in the July-September period, compared to 18.332 billion pesos in the same quarter of 2011.
America Movil recorded a 9 billion peso foreign exchange gain in the third quarter.
Analysts in a Reuters poll were expecting a net profit of 26.2 billion pesos in the period.
Quarterly revenue rose 4.5 percent to 192.821 billion pesos as the company added 4.1 million new wireless clients, a quarter of which stemmed from Mexico.
America Movil ended September with 256 million cell phone subscribers, stretching from the United States to Argentina. Adding fixed-line, broadband and pay television clients, its total accesses reached 319 million.
The company said it started including Dutch telecom KPN , where it holds 27.7 percent, to its results in the third quarter. During the period, the Mexican company also landed the acquisition of a 22.76 percent in Telekom Austria .
Brazil remained a tough challenge as America Movil continued to face strong competition from other players in Latin America's top economy: its fixed-line revenue helped offset declines in cell phone, service and equipment sales during the quarter.
Third-quarter earnings before interest, tax, depreciation and amortization (EBITDA) inched up 0.6 percent to 66.2 billion pesos but margins shrank.
"I think that the company is finding it difficult to position itself in the continent, it is investing too many resources into advertising, incentives, subsidies to lure in and keep subscribers, and that is punishing the EBITDA," said Monex analyst Valeria Romo.
The company shares slipped 2.01 percent to close at 16.6 pesos on Thursday before results were disclosed.