Well, this is interesting. iOS 6, pictured above on the left, is now able to scale to show five full lines of apps when displayed at 640x1136 -- the resolution a reported 4-inch iPhone would have.
iOS 5.1, which is on the right, only shows four lines when run in the same iOS simulator app. That's telling, since there would be little reason to add the support for additional lines if the screen was not going to get bigger. 9to5mac also reports that the simulator will not display the five rows at any resolution other than 640x1136. Other resolutions scale it to the iPad's home screen.
This is just the latest evidence that we'll see a 4-inch iPhone. There is a phalanx of iPhone rumours cramming itself down our throats, and almost all of them point to a taller, 4-inch model with the aforementioned 640x1136 resolution.
So it looks like big iPhones are coming in September, or at least extra real estate on your favourite iOS simulator's home screen. [9to5mac]