ENUM介绍

Telephone Number Mapping (ENUM or Enum, from TElephone NUmber Mapping) is a suite of protocols to unify the telephone numbering system E.164 with the Internet addressing system DNS by using an indirect lookup method, to obtain NAPTR records. The records are stored at a DNS database.

Although it facilitates calling VoIP users from IP and PSTN networks, ENUM is not a VoIP function and should not be confused with common VoIP routing based on SIP, H.323 or IAX protocols with a Uniform Resource Identifier (URI). 

more at http://en.wikipedia.org/wiki/Electronic_Numbering

http://www.enum.cn/cn/

http://www.enum.org.tw/

http://www.voip-info.org/wiki/view/ENUM