Always interesting videos on this channel, seldom telco related, now there is one:
https://youtu.be/4tHyZdtXULw
I just LOVE the history of the phone network. I read the book Exploding the phone by Phil Lapsley. The audiobook is narrated by a former phone phreak who happens to have tons of historical recordings of the network from "phone trips" he took with friends.
thanks for the book tip - did put it on reading to do list :-)