I remember when the Kinect was first released, and later when the first 3D AR demos leveraging Kinect Fusion style algorithms became public, thinking that this would be a very interesting thing to have on a mobile platform.
Now Google has made its Project Tango public that is promising to deliver exactly this.
Their protoype a 5″ phone is capable of tracking full 3D motion while simultaneously creating a 3D map of its environment. Running on Android APIs provide position, orientation, and depth data to standard Android applications written in Java, C/C++, as well as the Unity Game Engine.
Algorithms, and APIs are still in active development. You can apply for a developer program to receive one of the 200 prototype device currently available. They expect to distribute all of our their available units by March 14th, 2014.