In the US I don't know a single person that has access to POTS. Discord (with paid nitro) is the gold standard for quality and latency, followed by all the free VoIP apps
I live in the US, and I'm pretty sure everyone I know has a landline, though a good number of them are now digital/fiber/whatever. Some people I know still have multiple landlines, as it's cheaper than paying multiple cell bills if necessary. I know at least one person who used to have call forwarding set up to get calls on their cellphone, but with the current state of marketing calls they probably don't do that anymore.
Nobody pays multiple cell bills unless they wanna use several data-only eSIMs from different carriers to get better speed/coverage. If you just want a lot of phone numbers, you can port your numbers to a VoIP provider and forward them. Way cheaper than a landline
