Automatic Number Identification

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. 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".

Privacy note:

It is very important to realize that, when calling an "800" or other toll-free number, your telephone number can always be captured by ANI equipment at the "800" number site -- whether or not you would otherwise be able to "block" transmission of your telephone number via Caller ID. ANI overrides Caller ID blocking.

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.