OpenBTS is a simulator for base station of a cellular tower. When properly interfaced with a software defined radio (SDR), one can set up a small scale private network for research, and for special purpose applications. Here is a step by step guide on how we set up a small test bed. An FM bug is used to test the SDR set up.
References
1. D. Burgess, H. Samra, “The Open BTS Project” , 2008 http://cs.ru.ac.za/research/g09b0279/UsefulPapers/OpenBTSProject.pdf