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What: Shares of Latin American wireless carrier NII Holdings (Nasdaq: NIHD) plunged today, down by as much as 11% after the company reported earnings this morning.

So what: Revenue in the fourth quarter tallied up to $1.6 billion, a bit short of the market's expectation of $1.68 billion. However, the real shocker was the bottom line, and the loss of $0.05 per share was a big surprise compared to the $0.19-per-share profit that the Street was looking for.

Now what: The company added 467,000 net subscribers during the fourth quarter, but attributed the surprise loss to an unexpected rise in costs related to network deployment and marketing. Increasing competition led to higher spending to build its brand and retain customers. Forward-looking guidance also came in a tad light, with fiscal 2012's revenue forecast of $7.1 billion falling short of the $7.3 billion consensus.

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Fool contributor Evan Niu holds no position in any company mentioned. Click here to see his holdings and a short bio. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.