Ok, update time. This doesn't work quite as well as Mitel might make it seem in my opinion. I am seeing a success rate anywhere from 66% to 90% (daily). I wasn't able to find much documentation on this outside of the 9.0 self-study update course online, with good reason, there isn't anything out there. It took roughly three weeks for tech support to get the config right on this for my site, which is fairly straight forward.
The main thing that needs to be documented is that you cannot use fax profile 1, or compression zone 1. If you do so then the system will never go into T.38 mode.
As of right now, don't get it. Find another way to implement FOIP, at least until Mitel gets it together and stops charging to this commonly free feature.
I will post another update if things change with my success rates.