Since the Apple A4 was designed for mobile devices, and with the similarities between the iPad and the iPhone, it wouldn't be a stretch to imagine the 1GHz chip powering a faster generation of Apple's touchscreen phone. Nathan Brookwood, an analyst at Insight 64 says, "There's really no reason why a chip with this kind of characteristic wouldn't make it in the iPhone." Apple could even underclock the A4 in a new generation of iPhone which would allow for greater battery life. Currently, the iPhone 3GS uses an Arm based system on a chip produced by Samsung clocked at 600MHz.
Apple iPhone 3GS Specifications | Review