9to5Mac shows possible evidence of a larger screen for the iPhone 5.
Hacking the iOS6 beta emulator allowed them to test the theorised new screen resolution of 640 x 1136 px. Which showed a perfect five icon row iPhone home screen. Other similarly large iOS resolutions resulted in the iPads icon grid with much larger margins. It could be a coincidence, but evidence seems to be piling up indicating to a larger iPhone screen.