(Recasts; adds conference call details, analyst comment, background; updates share movement)

By S John Tilak

BANGALORE, July 23 (Reuters) - Latin American wireless carrier NII Holdings Inc (NIHD.O: Quote, Profile, Research) posted a better-than-expected quarterly profit, driven by 72 percent revenue growth at its Brazilian operations, sending its shares up nearly 12 percent.

NII, which operates in Mexico, Brazil, Argentina, Peru and Chile under the Nextel brand, has slightly over 5 percent of Brazil's post-paid market and sees huge growth potential with plans to invest $100 million this year in the region.

"We're only in the early innings of the growth opportunity in this country," Chief Executive Steven Dussek said in a conference call with analysts.

Earnings nearly doubled in Brazil on revenue of $330.3 million. The country had a monthly churn rate of 1.34 percent, the lowest among the coverage areas.

"Over time most of the explosive subscriber growth will come from Brazil rather than Mexico," Stifel Nicolaus analyst Christopher King said, referring to the company's current largest market.

Net additions in Mexico grew 33 percent. Consolidated churn, a measure of customer attrition, rose to 1.89 percent in the second quarter. Churn in Mexico was 2.36 percent.

The company, which uses Motorola Inc's (MOT.N: Quote, Profile, Research) iDEN network, added 394,500 net subscribers, its highest-ever, in the quarter.