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.

Best Buy, Sprint Nextel, and Wal-Mart are Motley Fool Inside Value recommendations. Apple, Amazon.com, and Best Buy are Stock Advisor selections. Motley Fool Options has recommended a bull call spread position on Best Buy. The Fool owns shares of Best Buy. Try any of our Foolish newsletter services free for 30 days.

Fool online editor Tom Cadorette holds stock in Apple, but not in any of the other companies mentioned. For its Memorial Day BBQ, the Fool's disclosure policy got a great deal at Wal-Mart on a gas grill, which it unfortunately set too close to the above-ground pool…