|The 3D IR sensor is on the bottom of the phone|
Update: Cnet publishes an interview with Remi El-Ouazzane, Movidius CEO. Few quotes:
"Over multiple iterations, we developed an architecture optimized for computer vision. The architecture favors parallelism, and not frequency. We're running [the Project Tango phone] on hundreds of megahertz, using a mix of hardware and programmable resources. On today's battery, running our processor will divide your battery power by a factor of 10."