Come next month there will be another retail outlet at which to wait in line for an iPhone. On Sept. 7, Best Buy will become the first U.S. retail chain to sell the iPhone, outside of the Apple-AT&T duopoly. The deal is an obvious coup for the big-box retailer, which has a national exclusive on the device (outside of Apple and AT&T stores) through Christmas. Just a few weeks back, Stifel Nicolaus Analyst David Schick suggested that availability of the iPhone only Apple and AT&T Wireless store