If you're into vintage telephone network sounds (and some really excellent technical descriptions of phone phreaking) take some time to listen to Evan Doorbell's recordings: https://www.evan-doorbell.com/

I grew up in the tail end of analog switches near my home. I remember the sounds of making phone calls changing over a few years. They became a lot less interesting and a lot more uniform. The sounds you'd hear calling the bigger towns in the area slowly took over the sounds you'd hear when calling smaller towns or out into the country.