Right. And even for phone numbers, there's a single authority
controlling the space. Internationally, it's the ITU; within the U.S./
Candadian zone, it's the North American Number Plan Administrator.
And its problem has been too little supervision -- see
http://www.bergen.com/biz/codes18200103181.htm
--Steve Bellovin, http://www.research.att.com/~smb