Intercepting GSM traffic

Paper's abstract:
"This talk is about GSM security. We will explain the security, technology
and protocols of a GSM network. We will further present a solution to build a GSM
scanner for 900 USD. The second part of the talk reveals a practical solution to
crack the GSM encryption A5/1."

Whitepaper.
Presentation slides.
Demonstration video.

Source and credits.