Just posted on the History of Phone Phreaking web site is a document of interest to, um, well, ok, only a few people: a 1975 edition of the AT&T Long Lines Traffic Routing Guide (TRG). But bear with me for a second because I think it's worthy of a moment's reflection, even if you don't find 60 Mbytes of scanned pdfs all that interesting.
Back in the 1960s and 1970s the long distance telephone network was made up of hundreds of electromechanical and electronic switches. A switch was a big machine; even a small one might take up an entire building. These switches routed long-distance calls over trunks, made up of communication links -- coaxial cables, microwave radio, or just plain old wires -- that connected switches together (click on the map for a high-res pdf):
To keep things straight, so that calls to Boise didn't end up in Boston or Buffalo, somebody had to keep track of all these switches and trunks. And that's where the Traffic Routing Guide came in. The TRG was the authoritative reference for how the network was laid out -- or how it would be laid out when a change was planned. The TRG was published by the AT&T Long Lines Traffic Routing Engineer in Kansas City, and it was updated frequently: pages were stored in loose-leaf binders and every page of every section number bears version information: "Section 1.2, 7th Revised, Page 1, issued: February 5, 1974."
If you were a phone phreak back in the day, a copy of the TRG was manna from heaven. It wasn't a tutorial by any means, since it assumed that you already understood how a lot of things worked, but it was the reference work for how calls got through the network.
One of the things I find interesting about this document is the realization that it wouldn't exist today in paper form. It would be a database, not a printed book. And indeed, the closest thing to the TRG is the LERG -- the Local Exchange Routing Guide -- and it's provided as a Microsoft Access database on CD ROM. Let's hope phone phreak historians in the year 2048 can read CD ROMs. :-)