Apple rumored to be testing a quad-core iPhone with a 720 display
Macerkopf also states that Apple is testing several different screen resolutions that are higher than the current resolution of 960x640. Specifically, it says that Apple is testing a 1280x720 display and a 1440x800 display. The first is seen in some Android phones, so it is entirely plausible. The second is somewhat of an odd ratio, but with Apple, you never know.
Obviously, coming off the release of the iPhone 4S, these are very early rumors. It will be interesting to see if any of these speculations end up holding any water in the future.
source: Macerkopf via Redmond Pie