[peterwwillis]

http://en.wikipedia.org/wiki/555_%28telephone_number%29

Much more interesting (from a hacker's perspective) were all the telco services provided using specific exchanges. For any given ILEC there was an exchange used for services provided to customers or employees, including everything from phone testing services and remote terminal access to business customer information and voicemail. By calling these numbers you could find some neat hidden services, and they were free from any phone. You can imagine how bored kids at school with a payphone could discover quite a bit in their spare time.

The DATU was my favorite. It was a secret lineman's number to test circuits, which also enabled you to listen in on live lines. Using these numbers without proper authorization meant jail time, but they had to catch you first :) Ringback was also a fun way to pass the time. Dial the number and hang up, and 30 seconds later the phone would start ringing, and i'd watch who would go answer it. Like I said, bored kids...

[larrys]

As a kid I remember these numbers we would call up and hear a bunch of other kids faintly having conversations in the background (and you could join in). Was many years ago perhaps someone else could fill in the details if they remember exactly.