Maybe not as old as Keith Roberts thinks, though. We had party lines when I was a teenager in the 1990s. I called them with our rotary, bakelite phone. I'd have guessed they died out with the advent of fiberoptics, but it turns out they still exist. Just not in your big city-centric reality. What, you thought the subway map marked the edge of the civilized world? Turns out there are still people living out there, and I'm not even talking about suburbs. I'm talking about isolated communities deep in the wilderness where you'd have to vespa for days to get a wireless connection.
Or, wait, maybe I'm reading this wrong and it's not about the cultural isolation of the incestuous Pluggers author/readership where they come to think something as blatantly unthoughtful as "Where did those party lines we used to have before we moved to the city go?" is a universally shared thing that everyone of their generation is thinking. Maybe it's about being so old you start believing your party's lines and actually value their rhetoric over their demonstrated interests, competence or integrity; that quoting a good-sounding soundbite is better than doing useful things like let's say keeping people from starving to death in the street.
I've seen that level of oldness. It's not pretty. But it's perfectly in line with what we expect from Pluggers.
Your humble critic's plugger status: Probably negative, sadly.