Barrett Lyon is an interesting guy. He’s the CTO & Co-founder of BitGravity, a company specializing in streaming media solutions for the web. Long ago I stumbled upon his blog which was then a very simple site. What caught my attention was a post detailing how to use direct dialing by SIP URI within Asterisk. It was unique because he laid out all the relevant DNS changes necessary, and supported the post with a video clip showing the process.
That old blog post has long vanished in a redesign of his site, but not long ago he replaced it with a new version called simply P2P SIP URI Dialing. It’s a good reference on the subject. Highly recommended.
Of course, dialing by SIP URI is really about wholly bypassing legacy telcos and what remains of their TDM networks. It assures that you have IP connectivity between end-points. That simple fact is what opens up the opportunity for wideband calling (HDVoice) as well as video calling and even encrypted calling.