Recently Google updated their XMPP servers to use standard Jingle for audio and video calls; see the “Google: The Future is Jingle” post on xmpp.org for some more details.
This would be good news for us, except that, by doing so, they broke calls in telepathy-gabble (so in Empathy, the N900 and MeeGo) in multiple ways.
Luckily GTalk developers were really cooperative and they agreed on fixing their servers and Will and Olivier already fixed Gabble too. The new version of Gabble (0.12.2 for the stable branch and 0.13.1 for the development one) should make calls work again on the desktop, MeeGo and on Harmattan (i.e. the N9 and N950) too.
For the N900 we don’t have any way to release updates, but Google will push an update to their servers (in the next week or two hopefully) with a N900-specific workaround.
Sadly video calls on the N900 will keep not working; the version of gst-dsp on the N900 doesn’t properly handle changes in the parameters of the stream .