A way to query E.164 numbers to keep calls "on-net".
These records can give you a pseudo redundant network. Allowing failover (or pseudo load-balancing) to other servers in your network.
E-Mail style phone numbers that more easily allow cross-domain calls to stay "on-net" without the need for a full keyboard on your telephone (i.e. analog telephones hooked up to analog adapters). A typical number will look similar to 123*543.
All of the following commands are input from the nsupdate command line. You should first have a key that you can use for updating a single zone.
update add 3.2.1.enum.org 60 NAPTR 100 10 "u" "E2U+sip" "!^.*$!sip:email@example.com!" .
If a user dials 123, this will route the call to firstname.lastname@example.org provided enum is correctly configured to use your zone.
update add 22.214.171.1243.freenum.org 60 NAPTR 100 10 "u" "E2U+sip" "!^.*$!sip:email@example.com!" .
(RFC 3263 is not too hard to read, for a change -- it's certainly shorter than RFC 3261, and it even has an ASCII art diagram :).