SO, we've got everything working except for the MWI lighting on the phones. We see a SIP NOTIFY coming from the UM, but get a 503 - Service Unavailable error on the UM from the Mitel system. I believe the SIP Trunk and SIP profile are configured correctly as we are able to leave a voicemail and get email notification. We have the extensions listed in the SIP Peer Profile Assignment form as suggested in another post in the forum. Any ideas as to why we are getting the 503 error from the Mitel?