Wal-Mart (NYSE: WMT) continues to expand its newly retooled cell-phone sales campaign in 600 or so of its stores throughout the U.S. The discount giant is displacing third-party wireless kiosks in favor of in-house departments with specially trained associates. Wal-Mart expects to have its homegrown efforts in all of its 3,600-plus U.S. stores over the next three years, with on-site sales and activation of wireless devices such as Apple's iPhone, with Sprint's HTC EVO 4G available in stores later this summer.

The push seems to be working rather well for the company. According to market research firm ComScore, recent consumer surveys show Wal-Mart in first place in the indirect retail channel of wireless devices, leading Best Buy (NYSE: BBY), Amazon.com (Nasdaq: AMZN), Radio Shack (NYSE: RSH), and Target (NYSE: TGT), for the period of March 2009 to March 2010.

The Bentonville behemoth is also dipping its toes in the fast-growing prepaid phone service market, with its StraightTalk brand (in a partnership with TracFone Wireless), and its newly launched Common Cents Mobile brand (with Sprint as partner). As the "Wal-Mart Wireless" initiative grows, and the company expands and diversifies its wireless offerings, investors should keep an eye on Wal-Mart as a key driver of the increasing commoditization of wireless communications.