For an example of an open-source GSM implementation that would allow one to build a base station, see http://en.wikipedia.org/wiki/OpenBTS http://en.wikipedia.o

For an example of an open-source GSM implementation that would allow one to build a base station, see http://en.wikipedia.org/wiki/OpenBTS http://en.wikipedia.org/wiki/OpenBTS . There are lots of videos about it on youtube where you can see it in action.