Osmocom + USRP

Hi Harald and all, I have a client who is interested in an USRP-based MS side implementation. I think that that OsmocomBB is a natural choice for the higher-level stack, but I have only vague idea about its current state. As I understand, burst coding/modulation, reference clock management and GSM clock management should be implemented to get a working MS. Is there anything else to implement? How well is API to Calypso DSP is abstracted in OsmocomBB? (Sorry for my brevity and no googling, I'm abroad on GPRS for few weeks)