I criticized the iPhone quite a bit, also because I am not a huge fan of touchscreens. In particular, because you have to put your sweaty fingers on the screen to interact with it, forcing you to keep cleaning the surface and, eventually, scratch it for good. On top of it, when you type, your fingers are covering part of the screen so you actually give up screen resolution.
The patent seems to solve most of these issues. For those who are familiar with patents (and have a lot of imagination), here you have the diagram.
For the rest of us, here's the idea. The front of the device is 100% screen (as the iPhone). The back is a force-sensitive touch-surface. That is: you move your finger on the back of the device and you see the cursor move on the front. So... you are actually not sweating on the front and your screen remains clean. And you do not cover your view while interacting.
Seems difficult to use? Have issues with hand-eye coordination? Well, you are using a mouse to scroll this page and you are not looking at your hand. You can make it. And the iPhone gets smaller and smaller, becoming mass market...
The iPhone nano, the biggest selling device of 2009.