By using cheap electronic components such as Arduino boards, you can pair them with your $400 phone to make an awesome robot. It would cost hundreds of dollars to add GPS, LCD's, motion sensors, wi-fi, cellular connections, speakers, and more to a hobby bot, but your phone already has these!
Together, the Android G1 and Arduino board allow you to use inexpensive electronics such as simple servos and sensors, to build powerful devices such as robots, remote telepresence, or fun toys for kids. More information at Cellbots.com.
Notice: This project currently requires an Android G1 with root access to use serial output from the phone to the Arduino robot. You can add a $20 BlueTooth module to your Arduino board to have the phone talk to it over serial BlueTooth if you want to use the commercial Android software.
Special thanks: We have the Hacker Dojo in Mountain View, CA to thank for putting us in touch, helping with some tricky issues via their mailing list of awesome members, and for having 74LS04 chips in stock. Most of the assembly was done at the Tech Shop in Menlo Park.