Google's Android OS maybe the best-selling smartphone platform, but on the nation's second largest wireless carrier, Apple's iPhone reigns supreme. AT&T today released its quarterly financial report and revealed that out of the 5.1 million smartphones it moved from April to June, 73% of them were iPhones. While no breakdown of iPhone models sold was given, many believe the reason for the 3.7 million Apple handsets sold was the iPhone 3GS being available for free. In the same quarter, Verizon managed to push 2.7 million iPhones. When the iPhone 4 is dicounted or given away for free, these numbers are sure to skyrocket.