Hi There, I'm a IT engineer with SDR (software defined radio) as a hobby and I'm fairly well educated on the hardware and software required to accomplish what you are looking for using open source software and hardware if required.
However I need to mention that you would be breaking laws in most countries using the GSM spectrum without a license, I'm happy to advice you on how to accomplish what you are looking for but I cannot be held responsible for what you do with that knowledge.
Thanks,
Ashwin