From VoIP.ms Wiki
I have added a Cisco IOS section for configuration of Cisco voice-enabled routers, using username/password authentication. The dial plan is extremely basic, but there's plenty of help around the rest of the internet for people to figure out a good dial plan.
The configuration shown should work on any voice-enabled platform running IOS 15.1(3)T and higher, such as the 2800, 3800, 2900, and 3900 series routers.
I just submitted a change for IAX2 configuration, because I wasted a good 4 or 5 hrs screwing around with my FreePBX setup in order to have incoming DIDs work. The problem was that my trunk was not named "voipms"! I know my formatting is a little off, but please ensure that error message I posted and the change is noted for future voip.ms customers. Thanks!
I have added some basic setup instructions for a Nortel/Avaya BCM 450/50 system.