Just finished installing an Asterisk server using Trixbox 2.2.4 between the Telco and a Nortel MICS system. I started with Nortel-Asterisk-0.2.pdf and it is a very good document to start with. It will help you find the information on your Nortel MICS using Nortels GUI admin software. Linked is the document of the modifications I had to go through to get it to work how I wanted.
My main goals:
1) Seamless to Nortel MICS Extensions
2) Seamless to Asterisk Extensions
3) Full call reporting for external calls
4) Leave the Nortel MICS in a state that it could be hooked directly to Telco if anything went wrong
Asterisk with Nortel MICS All goals have been completed and the system is working great.