Boris Smus, a student at Carnegie Mellon, built this elegantly simple robot that uses a smartphone to interpret commands from Twitter.
A few projects around the internet use an Android phone to control the Lego Mindstorms NXT brick. Most involve an ugly hack in which the phone communicates with a computer over WiFi, and the computer (paired to the NXT through bluetooth) submits the command to the brick. These projects typically use Android as a remote control for the NXT robot, and not as part of the robot itself.
This project does just that, while eliminating the need for a computer in the loop, so that the Android directly communicates to the NXT. This allows for more powerful Android-powered NXT robots. As an example, I made a fully autonomous twitter-controlled robot. The NXT uses two motors to spin in place or move forward, and a third motor to control the tilt of a Android phone cradle. The Android phone keeps track of its orientation (compass heading and tilt), polls twitter search for new commands and sends commands to the NXT brick. After each command completes, the Android phone takes a picture and sends it to twitter. Any twitter user can look at the last few photos, decide which command makes sense to perform next, and issue it.
[Via The NXTStep]