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.

Interested in more information about NII Holdings? Add it to My Watchlist.

Fool contributor Anders Bylund holds no position in any of the companies discussed here. The Motley Fool owns shares of Telefonica. Motley Fool newsletter services have recommended buying shares of Vodafone Group. 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 is investors writing for investors.