Digital Trends – Even though Android is the most popular Smartphone platform the iPhone 4 is the best-selling phone. A recent study shows that the second best-selling phone on the market is the over two year old iPhone 3GS, which is quite a shock. This news comes out even before we can see how effective Best Buyâs one day only iPhone 3GS sale going for the low price of nothing. As amazing as it is that the iPhone 4 is still the best selling phone on the market after over a year the fact that the iPhone 3GS is outselling all the new top of the line Android phones takes the cake.