ENUM is the unified method of mapping an E.164 number into an IP address, service or endpoint that can be used for communication. ENUM enables a party to be reached anywhere in the world using a single identifier, an E.164 number which at its simplest form is just a telephone number in international format(ITU-T). ENUM uses the Domain Name System (DNS) for storing and translating E.164 numbers into Uniform Resource Identifiers (URIs). For instance, DNS resolves the number 112-4567 into sip:packoy@telco.com when initiating a VoIP call.

Simply stated, ENUM converges the existing public switched telephone system and the IP network to enable users to find each other on the Internet using their assigned telephone numbers.