While I was on vacation, Aswath Rao published a pretty interesting piece titled OpenID Negates the Need for P2PSip. Here's what he's proposing:
I can store the IP address and the port number on which my SIP client will listen for incoming calls in a web page and my partner can visit that page before initiating a session request. This simple directory service almost eliminates the need for SIP proxies. Of course the problem is not fully solved because of the pesky NAT/FW traversal. If I am being served by a UPnP enabled router then the SIP client can establish the mapping rule; otherwise the web server can be used as the relaying point without requiring any SIP capabilities at all.
But with OpenID one can achieve something more. The web site can now provide the mapped IP address and port number by taking into account the OpenID of the initiator, just like Relevance Engine from iotum will do. What I mean is that the resultant mapping will be my SIP client for my family members and that of a voice mail server for business contacts, if the request is made on a weekend. I hope that after reading this Dean changes his mind regarding his remark about SIP not requiring the services of OpenID.
Very lightweight, and simple. He says that there will be an implementation available shortly. Cool!