According to reputable media outlets, including CNN.com, Best Buy will start selling 3G iPhones on September 7 in 970 of its stores. The decision by Apple was facilitated by the two companies' long-standing relationship and Best Buy's effort to upgrade its systems to allow for activation in the stores. Best Buy Mobile (a joint venture with CarPhone Warehouse Group) resells phone service on behalf of carriers, and already accounts for 3.6% of the cell phone market share. Expect that number to rise by the end of Q4.