There is a trick to the DNS - the DNS is a database. A domain name is an information token used to query the database; the DNS responds with information that normally happens to be IP numbers. Using a domain name I can find the IP address of a computer on the Internet. But if the database could contain anything, then I could add all kinds of address information into the DNS facilitating convergence. If I knew one piece of information, a domain name, perhaps I could get your SIP phone address, your other public telephone network numbers, your fax number, your IM address, your credit card number, your number on weekends while you are at the Cape, or any other address.
ENUM does this.
The next trick is that while a domain name can be anything, the ENUM folk associated ENUM domain names with public telephone numbers. The big prize this achieves as facilitating convergence between the public telephone network and VoIP. With one number, I could reach Fred at either his public telephone network phone or his Internet telephone. Neat trick.
Note that this does not turn the domain name into an actual public telephone number and it does not turn the Internet into the telephone network. ENUM is like a big address book. Ask it for an address; it provides you with an address. You still need to take the next step of acquiring communications service and setting up the communications. If you query ENUM and get a cell phone number, this does you no good if you cannot get on the cell phone network. Try that cell phone number on a different communications network and you will not get the cell phone. At the end of the day, an "ENUM number" remains a domain name which exists for the purpose of querying the DNS database.
ENUM numbers can be used anywhere. This makes ENUM international. Therefore the ENUM folk involved the International Telecommunications Union (ITU) which authenticates what countries are associated with what country code telephone numbers (The US shares the code "1" with several other countries). An ENUM query of a country code, such as “1”, is referred to that countries authoritative database; each country code would have its own – if there were more than one there is arguably a risk of inconsistencies and corruptions. By design there would be one top international authoritative database which refers to the top database for each country code (and that database can refer down as appropriate).
ENUM in the United States remains in its formative state. Particularly driven by those seeking to bind VoIP and public telephone network telephony, there are many interested parties hard at work. As the project has yet to truly hit the big show, proof of concept is absent. ENUM aggregates a great deal of personal data in the DNS database which is not necessarily regarded as secure. Some have criticized this as invasive of privacy and a possibly gold mine for telemarketers and those who seek to manipulate personal information. Other personal information aggregation services have faced troubles and been significantly scaled back. It is not clear that individuals are comfortable with the aggregation of their personal information. In other words, I give my home phone number to my son’s soccer team; I give my work number to my business contacts. But I do not necessarily want those numbers to mix in a way that an aggregated database might.
The Federal agencies involved are the Department of State which deals with the International Telecommunications Union, the National Telecommunications and Information Administration which deals with DNS, and the Federal Communications Commission which deals with the public telephone network. At this time, no formal proceedings have been initiated concerning or in order to implement ENUM.