Automatic number announcement circuit

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An automatic number announcement circuit (ANAC) 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 an ANAC works is fairly simple: A technician will call a local ANAC's phone number. 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. The main purpose of this system is to allow phone company technicians to identify which telephone line they are connected to. Because this system is based on automatic number identification (not caller ID) and 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 coherent system for them. Every telephone company (big or small) can determine its own ANAC for each individual central office, leading to a mish-mash of overlapping and/or spotty coverage.

In most North American area codes, 958-xxxx and 959-xxxx exchanges are reserved for various local and long-distance test purposes (a few may also reserve 999-xxxx); ANAC numbers sometimes appear in the 958-xxxx range but there is no requirement that they reside there. Other local test numbers may include ringback (to test the ringer when installing telephones) and loop lines (which connect a call to another inbound call to the same or another test number). Some carriers (such as Bell Canada) have been known to program payphones to disable calls to 958 or 959 test lines.

Some large telephone companies have toll-free numbers set up, but these numbers remain undisclosed to prevent abuse.

In early years some companies changed their ANAC number every month for secrecy. In one example of this concern, most payphones are assigned a telephone number and can ring if the number is called. The phone can then be used to make and receive calls by anyone, making it potentially useful for anonymous criminal activity such as drug dealing. Where a payphone does not have any number listed on the unit, the number could be discovered by calling an ANAC service.

Late in the 20th century Caller-ID and prepaid cellphone service became commonplace. These services being more easily exploited for criminal purposes, this type of abuse of payphones faded from concern.

There are some private national toll-free numbers that use ANI 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 phone you are calling from so that a computer can automatically pull up your account for the next available customer service representative. 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.