The majority of us continue to use our telephones with little thought to the limitations inherent in the numbering system we have grown up with. These phone numbers, however, associated as they are with the current PSTN system, are inadequate for IP-based service delivery. This means a complete re-think is necessary if we are to map numbers to the next-generation SIP and IM worlds while still retaining compatibility with the bulk of existing phone equipment. Try entering a URI using a standard DTMF input method!

A key weakness in the current world of phone numbering is that is not possible to assign yourself a number without purchasing services from a network provider. Numbers are also geographically linked and artificially limited in quantity. A new approach is needed.

One solution is ISN (ITAD Subscriber Numbers). This is a standards-based numbering system that is free, protocol-agnostic, delivered via DNS, highly scaleable, easily managed, easily implemented, and compatible with almost any iPBX or SIP proxy platform as well as other NAPTR addressable protocols and application delivery systems. John Todd explains how enterprises and service provider networks can become part of this quickly growing public numbering plan. He is also keen to explain why they should join.