We regularly get tweeted questions as to when the GDR2 handset will start hitting Windows Phones. Unfortunately most carriers are not very forthcoming about such information, but Australian carriers seem to be a bit more open than most, which makes things a bit easier.
Telstra have posted this handset update schedule, which reveals that the GD2 update for the Nokia Lumia 920 is currently in testing there, and should hit handsets by the 18th August.
It is likely testing is running a similar time line on other carriers, meaning we should see updates starting to roll out for most handsets in August. This is of course barring any issues such as the HTC 8X experienced, which may delay things.
Thanks dhillon for the tip.