When I logged into my callcentric account today, I noticed they now have "extensions". You can create additional sip trunks identified by a separate phone# and password, thus making it easier to route things on the pbxes.org side.
Before I had to create a sub-pbx with a separate sip uri and forward the DID from callcentric to this uri to be able to tell which number my call was coming from. Now I can simply create separate inbound trunks, create separate inbound routing for each of the trunks. I just though those of you on callcentric might like to know this.