9971/9951/8945 and other video phones Exchange Unified Messaging fast busy/busy tone/not working

Hi Guys

As per the subject and mostly for me/you as well, when working with Exchange Unified Messaging and certain models of phones you might have issues with a fast busy tone when trying to check the voicemail.

Easy answer to this: you are probably enabled for Video, for some reason if you try and negotiate a video codec with Exchange 2010 it will fast busy on you, so either disable video on the phone OR create a region for the Exchange UM SIP trunk so that it doesn't use video.