Google decided to make the Jingle open protocol ( XEP-166 and XEP-167 ) the default signaling protocol in GTalk. At the same time, support for the old protocols for backward compatibility will continue. However, they still recommend that third-party clients switch to the libjingle library, because SIP support will not last forever.
Now GTalk calls from GMail, iGoogle and Orkut are already being made via the Jingle protocol, the corresponding update for the Android application will be released soon. There are no plans to update the desktop application for Windows even in the future. It seems that the Windows client will not be developed at all.
Jingle is an XMPP extension that allows audio and video data to be transferred between two clients. Developed by Google in conjunction with the XMPP Standards Foundation.