A feature provided by the public telephone network to transmit the telephone number of the caller to the recipient. An individual may buy a telephone device displaying the number or he or she can dial a service code to hear an automated voice read the number of the most recent caller. Some Internet Service Providers (ISPs) and many corporate dial-up services providing dial-up access identify their customers on the basis of the Caller-ID to prevent abuse of the account by nonauthorized callers and to bill the connectivity to the correct user account.

See Also: Authorization; Internet Service Provider (ISP).