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Microsoft CEO Satya Nadella admits giving up on Windows Phone and mobile was a mistake
(www.theverge.com)
This is a most excellent place for technology news and articles.
They did try to do that, but there wasn't enough interest from companies to split their development teams to support a third platform. In fact Microsoft realised this and was so invested in it that they had a program where they would use MS devs to convert/build from scratch your iOS/Android app to run on Windows for free. All you had to do was take it over and maintain it after; almost no one took them up on it.
One of the clients I worked for had an interesting relationship with both Microsoft and BlackBerry at the time: both companies just outright paid them to build and maintain the Windows Phone and BlackBerry 10 apps, respectfully. Another agency did Windows Phone, but we billed them directly for the BlackBerry port of the Android app and its maintenance.