Looking for something else I found Blue Box: The VoIP Security Podcast which talks about (lack of) VoIP security. I love the name, it refers to attacks on telephony systems being something of all ages, independent of the actual technology. The new age of VoIP just makes new attacks possible. And with different queries I found Blue Boxing Comes to VoIP in the wired archives. "Phiber Optik" has written a module for Asterisk to make it accept MF (and be bluebox-able).