E.164 Number Mapping (ENUM)
ENUM is a system that uses the DNS to map ordinary telephone numbers (in the international E.164 format) to internet addresses for services such as VoIP.
What is E.164 Number Mapping (ENUM)?
ENUM lets a call to a phone number be routed over IP by looking up the number in DNS. Public ENUM saw little take-up, but private "carrier ENUM" is used between operators for routing IP voice traffic.