Automatic number identification is a feature of Inward WATS Service (Wide Area Telephone Service) which permits subscribers to display or capture the telephone numbers of calling parties. ANI service was created by AT&T for internal long-distance billing purposes, and is not related to newer Caller ID services. Inward WATS Service is purchased by businesses so that prospective customers (for example) can call the business toll free. The business is issued a distinctive telephone number beginning with a special area code such as "800" or "888".

A related piece of information conveyed to the "800" service subscriber is the DNIS or Dialed Number Identification Service. This is the number that the caller dialed when accessing the "800" service. With the information, the service provider can have several "800" numbers directed to the same call center and provide unique service based on the number dialed.

Privacy note

It is very important to realize that, when calling a telephone number, your own telephone number and telephone line type can always be captured by ANI equipment at the destination site -- whether or not you would otherwise be able to "block" transmission of your telephone number via Caller ID. ANI does not depend on Caller ID, therefore Caller ID blocking does not affect the delivery of your telephone number to ANI service subscribers. The destination telephone company switching office will always know the originating telephone number, and can relay that information to those who subscribe to ANI delivery services. Toll-free "800" number subscribers and large companies normally have access to ANI information, either instantly via installed equipment, or via a monthly billing statement.

Bill collectors and private investigators have often conducted skip tracing of missing people by sending them postcards, enticing them to call their "800" numbers. The "skip" reveals his or her whereabouts by dialing the number. Residential subscribers can also obtain access to ANI information through third party companies that charge for the service.

Similar Services in Other Countries

• Europe: Calling Line Identification (CLI)
• UK: Caller Line Identification (CLID)