There aren’t any actual figures out there with how many Windows Phone devices that have been sold, but the amount of Facebook users that have been added may be an indicator. Once you add the new users in, the amount of active Windows Phone Facebook users is around 8-9 million. Again, it’s not official, but the popular app is a way to measure how many Windows Phone devices that have been sold. If this is accurate, that means Microsoft may find that Windows Phone could cross the 10 million mark in the near future.

Source: WMPoweruser