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 numbers, numbers with caller ID blocking, and numbers with no outgoing calls allowed.
Some ANACs are very regional or local in scope, while others are state-/province- or area-code-wide: there appears to be no consistent national system for them. Every telephone company, whether large or small, determines its own ANAC for each individual central office, which tends to perpetuate the current situation of a mess of overlapping and/or spotty areas of coverage.
In most North American area codes, telephone numbers beginning with 958 and 959 are reserved for internal testing; some companies also reserve numbers beginning with 999. Numbers within this block are used for various types of local and long-distance testing; generally, this block includes a ringback number (to test the ringer when installing telephone sets) and a loop around (which connects a call to another inbound call to the same or another test number). ANAC numbers (the topic of this article) can also appear in the 958 range, but there is no requirement that they reside there.
Some carriers (such as Bell Canada) have been known to disable payphone calls to 958 or 959 test lines: in the specific case of Bell Canada, the system-wide ANAC line is at 958-2622. Some large telephone companies have toll-free numbers set up. In most cases, these numbers remain undisclosed to prevent abuse, but MCI maintains this widely-published, toll-free ANAC: 1-800-437-7950. This is distinct from technical support and other lines which use ANI so that a computer can automatically display the customer's account on a "screen pop" for the next available customer service representative: the MCI number above is intended specifically for use as an ANAC.
Formerly, some companies changed their ANAC number every month for secrecy; this is still the case with a few numbers. In one example of this concern, most payphones in the USA 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 a potential tool in anonymous criminal activity such as narcotics trafficking. Where a payphone does not have any number listed on the unit, the number can 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. In Canada, this behaviour has always been more difficult. As a matter of course, incoming calls to payphones are disabled; furthermore, the Bell ANAC number is also disabled.
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