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) popped more than 21% Friday after the company announced a deal with Apple (NASDAQ:AAPL) to bring both the iPhone 5s and iPhone 5c to its Nextel Brazil customers beginning Jan. 31, 2014. Apple shares were little changed following the news.

So what: Merely being able to offer Apple's latest phones should go a long way toward helping consumers in Brazil to think of Nextel as a more promising mobile carrier -- especially as the company has struggled to profitably compete with larger rivals in the country.

This also mark's NII Holdings' second big jump since Monday, when it signed an agreement with Telefonica, which will provide wholesale voice and data services to both its Nextel Brazil and Nextel Mexico subsidiaries.

Now what: Even so, NII Holdings stock still sits around 70% below its 52-week-high, leaving plenty of upside for investors if the company can manage to once again achieve sustained profitability. From a long-term perspective, I personally prefer to see more concrete evidence of its turnaround coming to fruition before I'd be willing to open a position myself. However, I can certainly understand shareholders' optimism in bidding up the stock today.

Fool contributor Steve Symington owns shares of Apple. The Motley Fool recommends and owns shares of Apple. 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.