EnableSecurity VoIPPack is a pack or addon for Immunity CANVAS that complements this tool with commercial-grade VoIP scanning capabilities. Probably the most intruiguing module currently is sipautohack.
The following is a taster showing sipautohack scanning a target network, identifying PBX server, enumerating the extensions intelligently and finally cracking the password for each extension on the PBX. More demos here.
For more information about VoIPPack take a look at the product page. EnableSecurity is currently running a private beta. Apply as a beta tester.