Hello Holger,
Couldn't we use a GNU-Radio combined with the GSM-HF-RX? We had a student research project which used that with Wireshark. I think I could borrow it for a few days and sniff some stuff at our lab. Just tell me what sequences you need.
You mean the USRP ? As far as I know its no big problem to save the raw RF data with it but there is no easy-to-use software yet to get nice traces from those data (e.g. extract all the different channels like BCCH, CCCH and so on) which for example could be used to see the messages between the BTS and the phone. I am not interested in the traffic (speech or data), just the signaling on the Air-Interface would be nice to have. But lets see what the future brings, projects like airprobe.org might fill this gap.
Best regards, Dieter