While Microsoft’s investments in the platform were headlined by a major partnership with Nokia (whose Lumia series of smartphones, including the Lumia 520 in particular, would represent the majority of Windows Phone devices sold by 2013) and Microsoft’s eventual acquisition of the company’s mobile device business for just over US$7 billion (which included Nokia’s then-CEO Stephen Elop joining Microsoft to lead its in-house mobile division), the duopoly of Android and iPhone remained the dominant platforms for smartphones, and interest in Windows Phone from app developers began to diminish by mid-decade. Microsoft laid off the Microsoft Mobile staff in 2016, after having taken a write-off of $7. 6 billion on the acquired Nokia hardware assets. Microsoft began to prioritize software development and integrations with Android and iOS instead, and ceased active development of Windows 10 Mobile in 2017. In 2020 Emperion teased a Windows phone that runs Windows 10 on ARM via Twitter. However Windows ARM cannot make phone calls but can run Android apps without switching OS or using an emulator.