ENUM is a system that converts an E.164 telephone number into a DNS name, then uses DNS records to discover the URI for a call. In practice, the number is rewritten into a domain-style label and looked up for routing data, such as where a SIP or VoIP session should be sent.
This matters because call setup depends on trust in the naming layer, not just the endpoint. If ENUM records are altered, hijacked, or poorly delegated, traffic can be routed to the wrong service, enabling interception, fraud, or denial of service. Defenders protect ENUM with tight control of authoritative zones, careful validation of routing records, and DNS security mechanisms such as DNSSEC where available. In attacks, the weakness is often not the phone number itself, but the trust placed in the DNS-based translation that follows it.