I followed your instructions...
I set up his workstation as a remote workstation in Interaction Administrator and assigned it the phone number of the nortel phone. I tried assigning it both just the internal extension of the nortel, and the external number. Either way, when the user logs into the machine with I3 and selects remote workstation, puts in the pc name and leaves the phone number blank, when someone calls his extension, the I3 client shows the popup for the incoming call, but his nortel phone doesn't ring. You can't pick it up on the I3 client (obviously) and when it rings for a while, it just goes to the voicemail of the Nortel phone. So, I know that it is trying to get to the Nortel phone, but it just isn't ringing. You can call the Nortel from any other Nortel, or I3 phone.