It's time again. The opposite of well is meant well. A thing that looks like a good idea at a first glance will stab us in the back. Definitely.
RFC2916 describes the permutation of E.164 numbers in DNS. This permutation is needed for IP telephone calls, to be independent of the protocol and to be able to find the people by their number.
So far, so bad: Exactly this protocol independence it is that holds the problem: Already in the specification there are examples which should get you thinking:
IN NAPTR 10 10 "u" "sip+E2U" "!^.*$!sip:firstname.lastname@example.org!" .
IN NAPTR 10 10 "u" "mailto+E2U" "!^.*$!mailto:email@example.com!" .
IN NAPTR 10 10 "u" "http+E2U" "!^.*$!http://svensson.ispa.se!" .
IN NAPTR 10 10 "u" "tel+E2U" "!^.*$!tel:+46-8-9761234!" .
That's nice. One does have a telephone number and gets the email address and the URL. Currently these entries aren't delegated but you can be assured: The telephone companies whose numbers these are are going to maintain the entries. Thus you will find the name and also the postal address in here, if not even more. This might sound rather pesimistic but after my cellular number appeared in a public telephone book without being asked at all I don't consider this utopistic.
Privacy protectors of the world, unite! This must not happen. As long as the phone companies are going to inform their customers it is a non-issue if the data really don't appear there. But it was never that easy before to automatically retrieve data of an unnumbered amount of people....