As I have not been able to find any way to submit a support case to Cisco regarding these phones, and in hopes that someone from Cisco may see this, I'd like to request full support for RFC 4235 in the SPA-50x series phones. This is so that in SIP proxy environments the SPA phones can provide their own presence information to the server. The server would SUBSCRIBE to the phone, and the phone would send NOTIFYs of type application/dialog-info+xml whenever there is a state change (ringing, on the phone, etc.). The acceptable Expires time received in a SUBSCRIBE should also be allowed to be VERY short (1 second) so that if the proxy needs to only see what calls are ringing on the phone in order to intercept them, it won't have to make a persistent subscription to the phone.
I have attached a packet capture showing how Polycom sends NOTIFYs on state change in accordance with RFC 4235. If anyone knows how to get this information to the Cisco SPA team for review I would greatly appreciate letting them see this.
If you have any questions post here and I will attempt to answer them.
