Doesn't this exist already? It's called DNS, along with E.164 representation of numbers.[0] You can map a telephone number to its E.164 representation by revers

Doesn't this exist already? It's called DNS, along with E.164 representation of numbers.[0] You can map a telephone number to its E.164 representation by reversing it, so +447123456789 would become 9.8.7.6.5.4.3.2.1.7.4.4.e164.arpa and delegation at various points in the hierarchy would be done by the responsible PTO or telco, so that looking up the number would map to a SIP or similar identifier. Alternatively, looking up a DNS name could return a record with the E.164 address as a CNAME or similar, to provide the name to number mapping. I don't think this is really very widely implemented, except maybe for some VOIP providers, but since 4G UMTS is IP based maybe it could become more useful? [0] https://en.wikipedia.org/wiki/E.164#DNS_mapping_of_E.164_numbers https://en.wikipedia.org/wiki/E.164#DNS_mapping_of_E.164_num...