Modern ANI has two components: information digits, which identify the class of service,[5] and the calling party billing telephone number.
Modern toll-free telephone numbers, which generate itemized billing of all calls received instead of relying on the special fixed-rate trunks of the Bell System's original Inward WATS service, depend on ANI to track inbound calls to numbers in special area codes such as +1-800, 888, 877, 866, 855, 844, and 833 with 822 reserved for future toll free use (United States and Canada), 1800 (Australia) or 0800 and 0808 (United Kingdom).
Toll-free subscribers and large companies normally have access to ANI, either instantly via installed equipment, or from a monthly billing statement.
[citation needed] ANI is used to provide automatic number announcement, a test facility of a central office for telephone installation technicians.
For example, toll-free service can be configured to send a specific DNIS number that is assigned to callers from geographic regions based on city, area code, state, or country.