You might like Evan Doorbell's YT channel then – he has a lot of old tapes from his misspent youth traveling the world on Ma Bell's dime, and has posted a lot of videos explaining it all for a generation (like mine) without any frame of reference.
Shameless plug: if you like his stuff, you might also like my book, "Exploding The Phone", which is a history of phone phreaking. https://explodingthephone.com/
Evan narrated the Audible version. :-)