By using computer vision techniques like motion blur detection and optical flow it is possible to detect up to 6 degrees of freedom.
They have developed three entertainment applications to explore this application domain. The first is a simple single player "Pong" game. The second is a "Doodle" application that demonstrates the various degrees of freedom. The third is a multiplayer version of the "Pong" game that leverages the Bluetooth capabilities available on many camera phones.
As it is using the camera on the phone to detect the motion, the camera must be at least responsive and fast enough to run the computation.
source: http://www.slashphone.com
