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 NII Holdings (Nasdaq: NIHD), which runs mobile networks in Latin America under the Nextel brand, opened Tuesday trading 11.1% below Monday's closing price. Shares have climbed back to a lesser 2% fall since then on low volume; the initial plunge was the only heavy action all morning long.

So what: Mizuho downgraded NII from buy to hold. The stock has fallen 34% over the last month as Morgan Stanley also slapped a hold tag on the stock, which was followed by a buy rating but lower target prices from Stifel Nicolaus.

Now what: Latin America is clamoring for wireless services, and NII knows how to create value for shareholders. To be sure, the company faces heavy competition from much larger operators America Movil (NYSE: AMX), Telefonica (NYSE: TEF), and Vodafone (NYSE: VOD). However, margins are rising even as sales growth accelerates. NII can hold its own in this tough market and looks like a deep value today. The only downside is a marked lack of dividends, which is unusual for a major telecom stock.

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