Karsten Nohl and Silvain Munaut demonstrated a toolkit which allows them to eavesdrop on any phone calls or text messages made on GSM network at the Chaos Communication Congress (CCC) in Berlin. GSM mobile phone networks are becoming the backbone of communications and commerce in the developed and developing worlds, but those networks may be easily susceptible to eavesdropping. The researchers claim the reason for their research was to raise awareness about and illustrate insecurities to Mobile Phone companies. They did not release all of the information used to carry out their research at the conference, but admitted that it would not be very difficult to recreate the parts they left out of their presentation.
Source: https://threatpost.com/eavesdropping-gsm-cheap-and-easy-123110/74813/