[runjake]

For starters:

http://en.wikipedia.org/wiki/Mark_Klein

http://en.wikipedia.org/wiki/Room_641A

http://en.wikipedia.org/wiki/Gsm#GSM_service_security

  GSM uses several cryptographic algorithms for security.
  The A5/1 and A5/2 stream ciphers are used for ensuring 
  over-the-air voice privacy. A5/1 was developed first 
  and is a stronger algorithm used within Europe and the 
  United States; A5/2 is weaker and used in other 
  countries. Serious weaknesses have been found in both 
  algorithms: it is possible to break A5/2 in real-time 
  with a ciphertext-only attack, and in January 2007, The 
  Hacker's Choice started the A5/1 cracking project with 
  plans to use FPGAs that allow A5/1 to be broken with a 
  rainbow table attack.