Apple may be looking at some different iPhone form factors in the future according to a patent application called “Dual sided trackpad”. The patent shows a device with a translucent cover. This cover would be touch-sensitive on both sides, allowing it to be used when the phone is open or closed (and covering the main display). Essentially, when the phone is closed, you have something similar to the current iPhone but potentially much smaller. Open it up and you have access to two touchscreens. For example, when the phone is open, the bottom portion could act as a dial pad.
The patent is not limited to mobile phones and could easily be used in future iPods, notebooks, tablets and more. For example, imagine a notebook where the touchpad is that patented translucent dual-sided touchscreen. Open, it would function like any trackpad today. But close it and it could work as a small external touchscreen display.
Unwired View has got some Photoshop renderings of what such an iPhone could look like.