>but a lot of them are reused when a subscriber changes provider
OT, but I had a not-so-nice experience with that. Some years ago I got myself a data-only phone number/SIM card for my 3G dongle.
It turned out that the number was reused, and the previous owner of that number had subscribed to a pay-for message service for upcoming events (concerts, movies, etc). And they kept arriving to my data-only dongle, and I didn't notice for a while. Had to pay for it, though.
I don't remember how I eventually managed to turn that off (the software for accessing/manipulating that part of the dongle was Windows only).
(They could have always searched you by name, if you're worried about your identity then it makes sense to not connect your phone number to FB)