This micro-controller combines an 8051 core with a radio transceiver that can transmit 10mW on the 70cm band. Code for it can be written with the freely available SDCC (Small Devices C Compiler) and TI sell a cheap programming cable for it (hard to find on the website - product code CC-DEBUGGER, also not stocked by most distributors, will have to order it direct from TI).
Unfortunately using the built in FSK modem you are limited to a minimum shift of about 3kHz which is too wide for the filters on most ham radio receivers. To work around this we have found you can just manually change the carrier frequency setting (minimum step size 366Hz) and get a solid FSK signal at slower baud rates (we mainly use 50baud). Its a bit picky about register settings but working code is in our SVN repo. under badgercub or badger2/CC1111_firmware.
To get the uplink working you have to jump through even more hoops. Again the build in demodulator isn't really an option but we found that the built in digital RSSI feature could be hacked to demodulate 50baud OOK quite effectively. Basically we integrate the RSSI over a bit period and then have a discriminator to decide wether that bit should be a 1 or 0. With a 35W transmitter and a 7-element yagi (1/4 wave whip on the payload) we were able to successfully uplink a string from over 190km away.
Below is a graph of successfully uplinked strings plotting transmit power used against range from the ground station. This was taken on Nova 14, BadgerCub's first flight and first uplink test.