4 links
800 Service Management System
sms800.com
Information about the central database for US toll free number management.
Area Code Information
areacode-info.com
Detailed information on the history and current developments in North American NPA allocations.
International Numbering Plans
numberingplans.com
A collection of all international numbering plans in the world. Some features require a paid subscription.
Number Portability
ported.com
Collates information on the regional initiatives in place to develop number portability and number pooling in the US.