Thanks to some tweaks to the iOS Simulator application that is included in the iOS development tools, we were able to run the simulator at the rumored next-generation iPhone display resolution of 640 × 1136. We did this running both the current public release of iOS 5.1 and the upcoming iOS 6.0 The iOS 5.1 simulator displayed the home screen with a stretched set of four rows of icons. On the other hand, iOS 6 displayed five complete rows as our sources said Apple was testing for taller iPhone displays.
From those screenshots, it seems like iOS 5.1 is using the traditional auto-resizing properties1 of the views, whereas iOS 6 has been explicitly programmed to use an alternative layout, in a similar way to how developers create separate interfaces for iPhone and iPad.
Put plainer, the iOS 6 Springboard has been specially coded for this precise resolution, and this resolution alone. This is very convincing evidence for a taller next-generation iPhone.
1 This is also known as springs and struts layout.