Below are goodies that could not be included in the book due to space constraints. Enjoy.
Back in the 1970s, if you dialed a non-working long-distance number, you'd be treated to a recorded announcement that went something like this:
I'm sorry, we are unable to complete your call as dialed. Please check the number and dial again, or ask your operator for assistance. This is a recording, 5168.
The digits at the end of the announcement varied from one place to another. Phone phreak Evan Doorbell does a terrific job explaining the allure of these numbers — and the recorded announcements themselves — to his 13-year-old self back in 1970:
(The above borrowed with permission from Part I of Evan's multi-part series, "How Evan Doorbell Became A Phone Phreak," available at Phone Trips. It is well worth a listen.)
The digits were called "identification codes for recorded announcements" and sometime around the end of 1968 the Bell System made their use standard at the end of all trouble recordings. The first three digits were the area code and the next one or two digits the ID number of the particular toll switching machine where your call had gone south. The ID number 1 was reserved for a regional center, 2 or 3 for a sectional center, and 4 or greater for primary or toll centers. In essence, this was debugging information, in that it allowed an operator or toll test technician to localize where something bad had happened in the network.
The official list of identification codes for recorded announcements can be found in the two links below, one from 1975 (an AT&T memo) and one from 1980 (Notes on the Network):
Click on the images for pdfs.