Over at Nerd Vittles that Asterisk Guru Ward Mundy has posted a great how-to implementing ISN lookups with his popular PBX-In-A-Flash Asterisk distributions. It’s a great overview of ISN and ITADs, including Freenum.org.
ISNs are a novel approach to bridging the gulf between the worlds of legacy phones with traditional phone numbers, and the realm of SIP URIs. It’s a way of dialing something like a normal number and having it automatically be resolved to a SIP URI. This is easily implemented using Asterisk, especially when Nerd Uno shows you how.
All of this is an approach to transitioning from our current state into a time when SIP URIs are more commonplace. That would imply that more of what we think of as “phone calls” would transit a pure IP network. That fact is a major enabling mechanism for such improvements as wideband audio & improved call security, amongst many other things.