Wikipedia has good info on how RespOrgs handle this:

https://en.wikipedia.org/wiki/Toll-free_telephone_numbers_in....

Absolutely, when call hits local switch it can be terminated differently based on its location. Particularly pertinent for modem based services in the 90s. A single national dialup number would terminate on 100s of local pops and routing decisions would be done to keep traffic as local as possible.

Internet Thruway from Nortel allowed multiple ISPs to use the same local termination hardware; If I remember the details correctly, different national numbers could be terminated on the same box, with the subsequent IP traffic routed to the correct ISP.

Yes, the Intelligent Network was the big thing in the 1990s. It allowed for routing as you describe as well as calling cards and many other features: https://en.m.wikipedia.org/wiki/Intelligent_Network

Oh the joys of watching terminal logs with SS7 data frames!

Was there any way for the customer to somehow interact with SS7 frames?

We’ve had techs come to our home in Canada in the 1990s, and I remember being fascinated with their mystical toolbox phone that seemed to uncover hidden phone line functionality. Almost like the whip in Indiana Jones.

I don't think so, but who knows. In my case I was working at a telco so everything was very obvious at the dev environments.

911 and 0 (operator).

Yes, but it would usually be based on the first 3 or 6 numbers of your phone number. The first 3 are of course “area code” and the 6 are called “NPA-NXX”. This has blurred some due to line number portability and cell phones.

Yes, at the very least 911 (US) / 112 (EU) run on that system. For SIP numbers routing depends on the address you set up in the phone provider's portal, so if you're using bring-your-own-SIP to provide landline phone service in your house, you absolutely have to keep the address current or you risk dialing 911 and ending up on the dispatch of your old addres...

Not in the US, but we had a country-wide number that each local station simply routed to a local extension. Sometimes, even multi-line wasn’t available at some stations, so it was just a sequential list of extensions to try. Looks like a hack, but it worked flawlessly.