The video on the next page features a prototype for an "invisible" iPhone created by researchers at the Hasso Plattner Institute in Germany. Basically, the idea is that with your iPhone in your pocket, you can hold your hand out and move your finger around on it as if you were holding your phone, and those movements will be picked up by a motion sensor elsewhere, and then sent back to your handset. In other words, just by moving a finger around on your empty hand, the plan is that you can answer and control your iPhone.
Unfortunately, the current implementation requires a camera to be mounted above you, and sends the signals back via Wi-Fi through another device as well, so it's not exactly easily usable (or cheap, probably). But the eventual idea is that the depth camera observing your actions would be wearable, so whenever you're in a situation where it would be more work to actually get out your phone, the camera would allow you to control things with just a few motions.
Seems interesting -- if the researchers working on the project can pull it off without you looking like a nut, poking at your hand.