The TIER research group at UCB is actively working on the OpenBTS project. The goal is to allow for easier programming of applications running concurrently with OpenBTS. This is done by modifying FreeSwitch to better integrate with OpenBTS.
We also have a running 10W BTS in the city of Berkeley covering campus and nearby areas. Contact us if you're interested in being a user of the system.
The lead developer is Kurtis Heimerl.