This is a special telephone number that is meant to be used by phone company technicians and other telecommunications technicians to determine the phone number of a particular line.
The way ANAC works is fairly simple: A technician will call a local ANAC's phone number (in Connecticut, they would dial 970) this number connects to a computer at a local [central office]? which uses a voice synthesizer or digital samples to "speak" the phone number of the line calling in. Ed Note: I believe that because this system is meant for phone company technicians, the ANAC system works with unlisted and even numbers with [caller ID]?blocking)
Some ANACs are very regional or local in scope, while others are state or [area code]?-wide. There appears to be no national cohesive system for them, leading to a mish-mash of overlapping and/or spotty coverage.
There are some private national toll-free numbers that use [Automatic Number Identification]? and then have a computer read back the number that is calling, but these are not intended for use in identifying your phone number, they are used in order for you to confirm the number you are calling from so that a computer can automatically pull up your account for the next available customer service representitive. However, if one were to call up one of these numbers, listen for the number confirmation and hang up, they would in effect be using this system as if it were an ANAC.
/Talk?