I meant no disrespect or other ill intentions, and certainly did not mean to come across as mean, I apologize if I offended you... and it is not a problem to ask for help if you don't understand something. My point was that if you don't have a grasp of how this is supposed to work, and how SIP works in general, you may want to involve your vendor for more assistance since troubleshooting through the forums would be very difficult. If a user here had been in this situation before they probably would have responded already, but since this is day 5 of the same problem and nothing has changed, it might be beneficial to work with your vendor.
If you could give some more information, like how your SIP Peer is configured in the Mitel and how your gateway is configured, it might throw a red flag to someone.