I think this fits the mood. The old telephone system was entirely analogue. It remained so well into the 1980s, even when they were carrying tens of thousands of conversations in parallel on a single wire or antenna.

When I was a kid, you could hear the white noise stack successively louder on a long-distance call, as it went through each additional link. And sometimes you could hear the hum of it all, just below the threshold of intelligibility. In hindsight it's amazing how well it all worked.

But sometimes it didn't work so well: https://vocaroo.com/1oCxkWyNDusp

Maybe a filter was slightly out of tune on that day. Recorded mid-1970s New York. The electronic beeps are in-band call establishment tones. (Yes, the same ones phone phreaks exploited. The recording was in fact made by one of those phreaks who has gone back and narrated some of his old recordings http://www.evan-doorbell.com/ )