You probably know this already, but you can use a cheap DVB-T usb dongle with a RTL2832U chipset to do a lot of things that used to require an USRP [1]. You can't transmit though.
Which is, unfortunately, a pretty big prerequisite for a GSM station. Raspberry Pi + DVB stick is a great combination for reception though, I've seen it used on autonomous model planes.
So they are using a DVB stick to broadcast the video stream back to monitor the autonomous model airplane, which is awesome. I tried looking for a site where hobbyists are doing this without luck. Can you link to a site where I can learn more about this specific use case?