This is the current list of things to discover about the usage of XMPP in Google Talk.
- What is the signaling protocol that they are using? They are using TLS so it’s not just a matter of sniffing the packets, but it should be available somewhere real soon now :);
- How are they advertising the Voice capabilities of each clients? This is another big one to deal with interoperable clients.
Updated as I discover all of this.