Telstra is relatively open about their update schedule, and have posted this table giving information about the impending Windows Phone 7.8 update.
As expected, the Nokia Lumia 800 update will go into testing soon, and should start rolling out on the 31st January.
The status for the other handsets are however a bit more iffy, with testing and update dates for the HTC Titan, HTC HD7 and Samsung Omnia W still to be confirmed. At least the handsets are on the list however, with expected availability being late February or Early March.
The dates confirm O2 UKâ€™s statement, who said the Nokia Lumia 800 update will be released at the end of January, and O2 Germany, who has confirmed the same date for the Nokia Lumia 710.
It seems Nokia handsets will likely be the first to benefit from the update before it is seen on other devices, possibly because they have given the customization of the software a higher priority.
Thanks Clyde for the tip.