Chris Paget, a security researcher who focuses on wireless and RFID issues, will give a demonstration of a technique that enables him to intercept calls made on GSM wireless handsets without any interaction with the user s handset. The technique involves using a device called an IMSI catcher, which is used in some law-enforcement intercept operations. Paget says he is taking a number of precautions to ensure that people in range of the device are aware of the demonstration and also that none of the data captured during the demo is kept.
Source: https://threatpost.com/researcher-show-gsm-intercept-attack-defcon-072610/74256/