Naming Authority Pointers, or NAPTR RR’s are used to map resources from the telephony world to the DNS. In conjunction with SRV records, they are used in IP telephony and VOIP applications within the context of ENUM.
It is not uncommon when using your registrar or web host provided DNS that some of the more esoteric record types, like NAPTR, are not supported. As the world moves toward internet telephony, VOIP and Session Initiation Protocol (SIP), expect to be using more NATPR records.