A good starting place to think about the CALEA system (besides, as other comments mention, looking at CALEA itself) is this paper from Matt Blaze and his students: http://www.crypto.com/blog/calea_weaknesses/

Also interesting is Steve Bellovin et al.'s excellent report on security implications of extending CALEA to VoIP: https://www.cs.columbia.edu/~smb/papers/CALEAVOIPreport.pdf Steve Bellovin is now the FTC's Chief Technologist and spends his days trying to bring technical sanity to the government in various ways.