Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Latin American wireless carrier NII Holdings (Nasdaq: NIHD) plummeted 18% today after its quarterly results came in well below Wall Street expectations.

So what: NII continues to add subscribers at a solid pace, but a disappointing bottom line -- earnings plunged a staggering 90% to $10.9 million -- reinforces fears over its long-term profitability. Rocketing costs continue to weigh heavily on margins -- operating margin narrowed to 11.5% from 16.9% -- suggesting that the competition in the space is only getting fiercer.

Now what: I'd cautiously look into this plunge as a possible buy-in opportunity. "We remain confident that the investments we are making in our business and our new networks will create value over the long-term by positioning NII to pursue a much broader group of customers," CFO Gokul Hemmady reassured investors. More important, with the stock now down a whopping 65% over the past year and trading at a forward P/E of 10, betting on that turnaround talk doesn't exactly come at a high price.

Interested in more info on NII? Add it to your watchlist.