I have a mixed environment.. both Nortels and Call Manager 6.1.2. The Nortels are Succession 4.5. To get IP working between Nortel and Cisco (including DTMF) we use AudioCodes. So it's Cisco SIP conneciton to Audio Codes, Audio Codes QSIG connection to Nortel. Works great. The only issue is caller ID from the originating phone (Nortel or Cisco). The remote end see the caller ID but the originating phone does not see the remote end's name. I know it's minor but it's one of those things that the end user is used to.