Dont have a ready reference material. Try your Cisco Account team I think they might try to hunt for some one out there who must have made sucha doc for other customers.
Btw.. Find a Integration document between nortel and Cisco below. This might be usefull is you want to move in phases to the new cisco solution and want calls to work to and fro between the system.
Hope this helps.
Just wanted to add this note to Deepaks good info.We are running this setup using a Nortel 61c as well.The connection's between the Nortel(NT5D12Ax Dual PRI cards) and Cisco (vwic on 2811's) are PRI's (using DMS100 protocol). We are running 25.40 on the Nortel.
For the Nortel side we use DSC (distant steering codes) that is where the CDP package comes into play, to move DN's across to the CCM when people migrate (works great!) That way our users don't need to dial any access codes or know where (CCM or Nortel) the called user exists. This method has been seamless and transparent. We have moved about 1600 users across to Cisco CCM so far, usually about 50 per night. It really works great! Buy yourself a good Barcode scanner to scan the new IP phones and use the Mac's to create a BAT file. Print out the Nortel DN/TN's ahead of time so you can match Toll Restrictions etc. The night of the cut, remove the Nortel phones, use the Distant Steering Codes (Load 87) to move the DN's across to CCM, run the BAT's for the new IP Phones, install the phones :) you are good to go!!
Here are some great docs;
Cisco Unified CallManager
Case Study: Nortel 61C PBX to Cisco IP Telephony Migration
From this good doc;
Nortel Meridian PBX and Cisco CallManager Integration
Cisco Unified CallManager System Guide, Release 4.2(1)
Cisco DPA Integration
Hope this helps! Let me know if you need additional info.