Also known as an
ANAC. It refers to a
number which, when called, reads off the number called from. It is used by
telco linemen to verify which
line they're working on, among other things. Used by
phreaks to verify which
line they're
beige boxing from, among other things.
This is often mistakenly interchanged with
Automatic Number Identification, which is actually a service similiar to
caller ID for people with
digital trunks.