If you like learning about telephone system, phone phreak Evan Doorbell has a very interesting series of podcasts about his time exploring the telephone system in the 1970's. The podcasts include his recordings from that time period.

It was neat to hear some of the old tones and recorded messages I grew up with, as well as ones that were well before my time:

http://www.evan-doorbell.com/production/group1.htm