Hacking Exposed VoIP Voice over IP Security Secrets and Solutions by David Endler and Mark Collier.

Here you can donload the security tools mentioned in the book. I have some books from this serie and think I might buy this one as well.

Though most of the reviews on Amazon are not positive. El Reg has some notes on it as well. (Yes I know that the picture isnt the right one for the cover of the book, but I could find the right one)