Telstra Australia has published table for handset software updates with expected roll out dates as well. According to the table the PR1.1 aka Portico should roll out to Lumia 920 by end of January. Similar timelines are mentioned for WP7.8 roll out to Lumia 800. Though there is no clear timeline for Lumia 610, but once the roll out commences for Lumia 800, it should not take much time from there.

Thanks Marc for the Tip. Cheers !!