Build Your Cellular Network-OpenBTS

The DIY wireless network space gathers steam from Fabfi covered earlier to OpenBTS:
Tech Review reports (subscr reqd):

The task of running a cellular network has usually been reserved for major carriers. But now an open-source project called OpenBTS is proving that almost anyone can cheaply run a network with parts from a home-­supply or auto-supply store. Cell-phone users within such a network can place calls to each other and--if the network is connected to the Internet--to people anywhere in the world.

On their website it is described as:

...an open-source Unix application that uses the Universal Software Radio Peripheral (USRP) to present a GSM air interface ("Um") to standard GSM handset and uses the Asterisk software PBX to connect calls. The combination of the ubiquitous GSM air interface with VoIP backhaul could form the basis of a new type of cellular network that could be deployed and operated at substantially lower cost than existing technologies in greenfields in the developing world.

photo courtesy of OpenBTS