I have something similar. The issue you are running into is that CallManager does not keep state of Asterisks channels. SIP trunks are wide open from the perspective of CallManager. I would suggest you create a hunt list and put the router in first. When the router is used up it will roll to Asterisk.
Might be coming at this from the wrong angle but couldn't you use Locations based CAC for this? Basically put your phones in one device pool with a different Location and your SIP trunk in another. Might need some tweeking to get the figures correct but could work for you.
SIP traces provide key information in troubleshooting SIP Trunks, SIP
endpoints and other SIP related issues. Even though these traces are in
clear text, these texts can be gibberish unless you understand fully
what they mean. This document attempts to br...
Please find the attached HTML document, download and open it on your PC.
This provides an easy to use form where you simply answer a few
questions and it will render the proper jabber-config.xml file for you
to copy/paste. There is built in logic to verif...
CUCM Database Replication is an area in which Cisco customers and
partners have asked for more in-depth training in being able to properly
assess a replication problem and potentially resolve an issue without
involving TAC. This document discusses the bas...