Up until about 3 months ago, all outbound calls from our switch carried the physical address for the location and a 7 digit number which AT&T considers our main billing number."
None of the above ever came from your switch. The 7 digit number could have been sent by the switch, but was more then likley sent by ATT.
The switch can send the CLID for each phone, but CLID tables will need to be setup and a list created containing the DID number, building location, location in the building ect. This is not a 5 min job.
The last placed I worked, we had all phones sending CLID but we never setup any thing else, so if the Fire dept showed up we had to figure out where the need to go.
This is a Signature and not part of the answer, it appears on every reply.
This is an Analogy so don't take it personally as some have.
Why change the engine if all you need is to change the spark plugs.