Microsoft has sold 4.2 million Windows Phone 8 handsets, according to Facebook data

We haven't heard from Microsoft officially on how many Windows Phone 8 devices the company has sold so far, but thanks to some external data and a little bit of math, it's been estimated that approximately 4.2 million Windows Phone 8 devices have been sold since October, possibly more according to other estimates.

According to The Next Web, there's a ratio that exists between the number of monthly active users of the Windows Phone Facebook app and the total number of Windows Phone handsets sold. Thanks to the ratio, the monthly active users figure can be used to figure out the number of handsets that were sold recently, since older phones wouldn't appear in the figures.

First off, monthly active users for this year is booming compared to last year, according to WMPoweruser. Around 627,000 monthly active users of the built-in Facebook app have been added since October 1, 2012 (the start of Q4). Over the same period last year, less than 150,000 monthly active users were added by December 15. That's four times as many users, which goes right along with Microsoft CEO Steve Ballmer's statement that the company is selling four times as many Windows Phone handsets than last year.

The aforementioned ratio is 6.756 handsets sold for every active user of the Windows Phone Facebook app, based on last year's sales numbers. This results in 4,236,012 Windows Phone 8 devices sold since the start of the fourth quarter. Obviously, the ratio may not hold as much weight as it did last year, but it's certainly a good starting point to the guessing game.

However, WMPoweruser suggests that Microsoft has sold more than 4.2 million WP8 devices. Research firm Gartner estimated that Microsoft sold about 2.75 million Windows Phone devices in Q4 2011. Using those same estimation techniques as last year, the data suggest that 7 million Windows Phone handsets were sold already this quarter, with a possibility of over 10 million being sold by the end of the quarter. Obviously, you should take these figures with a slight grain of salt, but it seems these guys are confident in their estimates so far.

[via The Next Web]