After a banner year in 2007, rapidly expanding Latin American wireless leader America Movil (NYSE: AMX) hit the skids in the first quarter of 2008, as its earnings growth disappointed investors. In response, numerous analysts lowered their ratings on the stock; U.S.-traded American depositary receipss in America Movil fell more than 13% the day following the earnings release.

It's not surprising that the company added "only" 5.7 million subscribers in the period, compared with 10 million in the seasonally strong fourth quarter. Nonetheless, service revenue in the most recent quarter was 20.8% higher year over year -- an impressive number, unless you expected numbers closer to 30% that the company has produced in recent history.

Investors may have been shocked most by a 5.5% drop in net income, driven partially by a 22.7% increase in costs year over year. Numerous other items taxed the bottom line, too, including interest expense and depreciation and amortization charges that grew much more quickly than revenue.

Rolling out next-generation (3G) wireless services across many of America Movil's Latin American markets has been expensive, but the company needs to keep up with main rival Telefonica (NYSE: TEF). It's also best to make these investments as soon as possible, since new services will bring in new revenue streams.

Around the world, 3G services are boosting margins and earnings for carriers such as AT&T (NYSE: T), Vodafone (NYSE: VOD), and Verizon (NYSE: VZ) and making up for dwindling revenue from traditional voice services. Value-added data services, coupled with hot smartphone products such as Apple's (Nasdaq: AAPL) iPhone and Research In Motion's (Nasdaq: RIMM) BlackBerry, are proving to be a killer combination for profits in mobile services.

So don't buy for one minute the notion that America Movil's best days of growth are behind it. Even though the market seems to be packing it in and moving on to other investments for the near term, the latest generation of advanced services is only now starting to roll out across Latin America -- a market that has proved quite receptive to wireless data services. Long-term-focused Foolish investors would be wise to keep tabs on America Movil for good buying opportunities.

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Fool contributor Dave Mock had his political career torpedoed early on, with the publication of compromising baby photos in settings he could have sworn were "diaper-optional." He owns no shares of companies mentioned here and is the author of The Qualcomm Equation. Apple is a Stock Advisor recommendation. The Fool's disclosure policy is the cherry on top of your investing fudge sundae.