[yig]

"LucidTouch: A See-Through Mobile Device" by Daniel Wigdor, Clifton Forlines, Patrick Baudisch, John Barnwell, Chia Shen. Published at UIST 2007.

paper: http://www.cliftonforlines.com/papers/2007_wigdor_lucidtouch...

video: https://www.youtube.com/watch?v=qbMQ7urAvuc

[raphman]

And more on this topic: "Back-of-device Interaction allows creating very small touch devices" by Patrick Baudisch, Gerry Chu (CHI 2009):

http://patrickbaudisch.com/projects/nanotouch/