I was curious if any AVRFreakers have any APRS systems. If you don't know what APRS is, here is a definition from http://www.aprs.net/:
APRS is a system developed by Bob Bruninga, WB4APR, which uses amateur radio to transmit position reports, weather reports, and messages between users
I was looking at making a modem with AVR based on WhereAVR at http://www.knology.net/~gdion/wh...
I was going to modify it slightly for use biking / hiking / driving, whereas WhereAVR seems to be for balloning (very little modifications needed, really).