That number is up on Canalys' Q4 2011 projection of 2.78 million devices, and happily breaks the five million units psychological barrier. It's also slightly over our estimate of sales for Q4:
I'm going to put a number out there for Q4 that I think would be a respectable number for Windows Phone sales to achieve, and one that would go some way to covering the major elements above. That number is five million handsets.
I wish I had a big spreadsheet that could show why I felt this number is a decent target, even if it is a little bit of a stretch. It's certainly far less than the dominant handsets can put together, and yes it's measured over 13 weeks where some feel a leading OS should be shifting that many handsets in a single month, or even a single week. But it's a start, with a number that builds on Windows Phone 7, shows an upwards direction, and will continue to build the ecosystem around a thriving platform.
What it doesn't quite match up with is Steve Ballmer's boast of 'four times' and 'five times' more devices after the launch of Windows Phone 8, and the festive season. At least not until you realise Ballmer is talking sales and Canalys are talking shipments.