There was a DEFCON talk two years ago in which the presenter assembled large antennas and ran open-source software that allowed him to mimic a base station. Eve

There was a DEFCON talk two years ago in which the presenter assembled large antennas and ran open-source software that allowed him to mimic a base station. Everyone who was using phones on a specific network (I don't remember which -- I want to say AT&T) connected to his base station within a few minutes, and he proved the concept by hijacking outgoing calls. >If one's phone stays in the same area, it will never transmit while idle. Maybe phones used to do this, but nowadays I'm not so sure.