NII added 327,000 net subscribers during the quarter, below analysts' consensus estimates of 350,000, noted Thomas Weisel Partners analyst James D. Breen.

He said the weakness in net customer additions came mainly from Mexico, due to disruptions from hurricanes and increased competition, and from Brazil. Breen nonetheless kept an "Overweight" rating on the stock.

"Despite lower than expected net adds in Mexico, we continue to believe that the company's growth prospects in both Mexico and Brazil remain strong," he wrote. Breen said NII remains his top pick in the wireless sector amid high growth prospects in Latin America.

Stifel Nicolaus analyst Christopher C. King, meanwhile, called the quarter "worse than feared" and said competition from Telefonica SA's Movistar unit in Mexico, along with weather problems, likely hurt results.

He nonetheless kept a "Buy" rating on the stock.

Deutsche Bank analyst Rizwan Ali called the stock price drop a buying opportunity.

"We believe the weakness in the quarter should not indicate a long term trend as the level of service and the technology offered by NIHD is still very attractive to its target market segment," Ali wrote.

In a conference call with analysts, Chief Executive Steve Shindler said NII expects to deliver more net subscriber additions in 2008 than in 2007.

NII offers wireless services under the Nextel brand.

Shares fell $13.39, or 19.3 percent, to $56.05 Thursday. Earlier, the stock hit a 52-week low of $52.51.