"[I]t's been digital switching and multiplexing for a very long time."
Yes, but it's been on a circuit-switched digital network. That's the magic of POTS---if you get a connection (which is roughly always), you have ~3kHZ of bandwidth of your very own, all yours until you or your interlocutor hang up. No worries about handing off to an overloaded cell; I get continuous service through power outages thanks to copper wires and walls of batteries back at the central office. That's why they'll only get my POTS by prying it...you get the Idea.
<rant>Why do people persist in buying flash and glitter which operates worse than the boring old stuff? I have friends whom I've given up on communicating with because I can't understand them through the distortion and interference, and can't hold a conversation with for the call dropping every few minutes. With any luck I'll be dead of natural causes before the telcos finally persuade their governments that the old service is so 1950s, no one needs it anymore.</rant>
Oh, yes, and for US$30 I get to talk to anyone in the country for as long as I like. Try that on a cell phone.