One of the biggest challenges I had in Exploding The Phone was to try to give some sense of what the old telephone network sounded like -- its "sonic landscape," if you will. I did the best I could, but it's hard to do it justice.
Fortunately, a couple of people have created a pair of lovely guided tours of the sounds of the old network, so you can experience them for yourself.
The first one is from ElmerCat and is titled "Sounds of Long Distance Calls." As he notes, "Today, every phone call you make sounds basically the same. However, back in the days of electromechanical switching, calls sounded quite different, depending on where you were calling, the type of local central office you were calling from, and the sometimes complicated route to get from one place to another..."
ElmerCat's web page gives a nice quick overview of old network sounds. Phone phreak Evan Doorbell has one that is a bit longer and more detailed:
Of course, if you're hard core about this stuff, you'll want to check out Phone Trips, the Internet's home for old network sounds.