Microsoft Research and Mitsubishi Research teamed up on a project called "LucidTouch" to reinvent the way touch screens work.
LucidTouch is a mobile device that addresses the current touch screen limitation (like small display sizes) by allowing the user to control the application by touching the back of the device. The key to making this usable is what the project team calls pseudo-transparency: by overlaying an image of the user's hands onto the screen (no, it's not transparent) an illusion of the mobile device itself is being semitransparent is created.

This pseudo-transparency allows users to accurately acquire targets while not occluding the screen with their fingers and hand. LucidTouch also supports multi-touch input, allowing users to operate the device simultaneously with all 10 fingers. The project team also presents initial study results that indicate that many users found touching on the back to be preferable to touching on the front, due to reduced occlusion, higher precision, and the ability to make multi-finger input.

No word yet if or when we will see this commercially available but this seems to be an interesting way to use mobile device "touch screens".

Cheers ~ Arne