911 certainly did exist before PRI's, however ENHANCED 911 as we know it today did not... E911 Operation Centers would flag account like yours with a note or other comment stating the 911 operator needed to verify ALI and ANI (Location and contact number basically) manually with the caller to get room, building, department, or whatever was needed to respond to the emergency call... it was a huge problem for college and large business campuses, factories, etc.
There was a time when you could setup Outbound Caller ID on T-1's, it cost extra (significantly if I remember correctly) and it was very different than the standard used with PRI's today, and it was a nightmare to setup as it had to be done in ARS with digit manipulation based on extension number and had to be coordinated with the carrier for each T-1 installation and was essentially a custom job... You would send inband information digits with a call, one I did once had to be like this:
*[10 Digit T-1 Billing Number]*[10 Digit DID outbound CID number]*[10 digit destination number]# (or some terrible thing very similar)
EVERY call had to be that way, whether it was local, LD or whatever, and International calls were a nightmare as well. But every carrier was different and had to custom build it each time, and now carrier just don't do that anymore, T-1's for voice are a thing of the past and it just isn't worth their time to go through the headache.
Some carrier do still do Inbound ANI on T-1's, but many have done away with that as well.
The best thing I can tell you is contact the carrier and ask them if they can/do support outbound caller on this customers T-1 service, if they say they can then will likely specify the format you need to follow exactly, what the cost involved is, implementation period, cut-over times, etc. since if they can do it, it will likely require a re-provisioning of the entire circuit, or they will just say no.
