For me the phone is provided by the cable company that also provides TV and broadband. I can't see it disappearing because it's a small additional cost once you've got the cable for those in place. Also I think wired comms is always going to have advantages over wireless.

Maybe I misunderstood what was meant by POTS. It is wired, and powered from the phone lines. I'm pretty sure it'd work if the household electricity failed, but I don't know about a wider failure or where it really gets its power from now. Interesting question.

Having the phone from the same provided as the internet means that if one fails, they'll probably both fail. However, it does act as a back-up to the mobile phone network. I'd have thought the under-ground cables would be more reliable than masts.

I suspect the only way to be sure of doing better is to get a satellite phone. Or a radio ham's licence. Neither of which I can be bothered with. The law of diminishing returns kicks in.