An American hacker has demonstrated how to intervene mobile phone talks. The necessary equipment includes a radio hardware valued at $1500 and a laptop computer. He showed his equipment broadcating GSM signals which makes mobile phones think that they are communicating with their communication provider company. He then connects to GSM provider and can record all the communication on his laptop. It was demonstrated on a hacker convention recently held in Las Vegas, NE, US.

Quoted from: here