Comment by consp
12 hours ago
It used to be illegal here to reverse look up a name matching to a phone number, since it was "owned" by the state telephone company and they didn't want that happening. But you were allowed to reverse look up the address of a number and then look up the person and match it to the number. So that magic happened under the hood. The trick was getting the residential information but since that wasn't a problem in the '90s I'm sure it is even less of an issue now.
When I was a kid there were reverse phone books that were indexed by number. Not common, and I think they were pretty expensive, but the IIRC the local public library had them.
When I was a kid in Sweden that was just part of the local phone book.