In what will surely be a boost to the company in its wireless retail efforts, Best Buy will become the first retailer outside of Apple-AT&T (NYSE: T) combo to start selling the iPhone. Both the 8GB and 16 GB versions of the iPhone will go on sale in most of its stores (about 600 of the 970 in total) starting Sept., except for stores located in areas where AT&T’s wireless service isn’t available, the company said. Stand-alone Best Buy Mobile shops, which have opened in about 15 U.S. cities, will also sell the device. Shawn Score, president of Best Buy’s mobile division is gleeful: “Quite honestly, many of our customers come to our store every day asking for it…We’re excited we’re going to be able to say yes,” he told WSJ.

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Best Buy has been expanding its footprint in wireless retail: just yesterday it announced airport kiosks will sell mobile phone and accessories. It two-year old deal with UK’s Carphone Warehouse is also doing well, at least according to the company: The JV sells handsets from a variety of makers and carriers help customers figure out which features they want and how to use them before they leave the store. For example, they will set up a customer’s email and data transfer and ensure it works. The retailer also said it had completed its roll out of Best Buy Mobile throughout its 965 US stores three months ahead of time.

AP: Last week, Best Buy announced it had completed a two-year conversion of its stores to include upgraded cell-phone departments under the Best Buy Mobile brand. It has upgraded its computer systems to handle cell-phone activation and spent 250,000 hours training its employees. Score said Best Buy Mobile, which resells phone service under the carriers’ brands, now has a 3.6 percent share of the cell-phone market, up from 2 percent last year.