Speaking at Microsoft’s Worldwide Partner Conference, CEO Kevin Turner said that there are now more than 12 million active Lumia 520 smartphones around the world (including Lumia 521 models for T-Mobile). Turner also mentioned that the 520 is the world’s best selling handset in its price range (sub $100) - though we’re not sure he has enough data to be absolutely certain of that.
Launched in early 2013, the Nokia Lumia 520 can now be purchased for as low as $50 (at least in the US). A successor to it - the Nokia Lumia 525 - was released this January, while another successor, this time running Windows Phone 8.1, might be announced in the near future as the Lumia 530.
Obviously, launching ultra-cheap Windows Phone devices is helping Microsoft a lot. We’ll see many more affordable WP smartphones from now on, as Microsoft opened up its platform to pretty much any manufacturer interested in making handsets based on it.