I'm in the progress of setting up a demo that involves a SIP registrar/proxy, a VSX7000 and some Telepresence M100 clients.
So far, everything "kind of" works, but there are two REALLY strange bugs the folks at Polycom may be interested to hear
Bug #1: The VSX 7000 in the REGISTER request sets the "To" header to simply "sip:username", without specifying the FQDN (e.g. sip:user@host). This way, the SIP registrar has no matter of understanding the name of the user as it interprets the string in the "to" header as only the host name. The VSX will then be registered as "unknown". Tried this with 3 different SIP servers, and the behavior is always the same: if you are lucky, the SIP server accepts the request and you will simply have an "unknown" endpoint that can make calls but not receive them, if you are unlucky the SIP server eventually refuses to register as it can't recognize the endpoint's name. You are forced to set up a static registration, which is by no means a good way to handle this.
Bug #2 (the most important,since this is a new product): If the M100 client is set up to use SIP over TCP, it correctly sends the REGISTER and INVITE requests over TCP, but when the client hangs up, the BYE request is sent over UDP, independently of the settings. Clearly, as the SIP Proxy is expecting a TCP signalling channel, the BYE request is not forwarded and the other endpoint does not clear the call.
I hope someone has an answer to this, I guess these are not difficult things to be corrected...