Wire is pretty much never removed once it’s laid out and I’m sure a lot of DSL based internet connections still run over same twisted pair that would have carried POTS lines.

But you’re probably right that there’s a VoIP device keeping these up and working, maybe just more than 6 ft away and instead in some Telco box down the street.

I think POTS installations will remain for decades more in niche cases - emergency backups in elevators, security systems, hospitals, fire departments. And evidently Grandma’s AOL internet connection up until this month haha