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.

A still-working Automatic Number Announcement Circuit number is 1010732-1-770-988-9664.