3. Most carriers in the Midwest use a Cisco IAD to take the Fiber connection and convert the SIP traffic to ISDN traffic and put it out on a T1/PRI interface.
Something like this is what I suspected. Thank you for breaking it down.
If I can trouble the forum for one other question (not sure if I should make a separate post), I want to have backup hardware for the HX 5000, in case there is a fire, flood, or theft (you might laugh, but true story: there is an HVAC unit above the network closet where the Mitel is stored, and due to the pvc drain of the roof HVAC getting flooded, the ducts started to leak moisture from the evaporation coils right onto the server racks. The Mitel actually got water on it, and shut off, but due to good water egress design on the case there was no permanent damage. Lesson: don't put a server rack in a room right below an hvac unit, and never build a case where water can drip down from above into the chassis).
So I bought a surplus HX 5000 with the same cards in the hopes of being able to factory reset, swap the compact flash, and then upload the backup db onto the new box. But I see some posts here mentioning that the box might be password locked. I haven't been able to investigate yet, but is what I'm doing feasible?