Hi ark5455,
Are you using a full Cisco CM to power the Cisco phone, if so you will need to run MGCP protocal between your gateway and the CM. If you are running H323 then it's not supported yet, but will be in the next IOS version. If your already running MGCP make sure you are using the RCAP setting QMWI between the CM and the Nortel.
Markoj!