Microsoft (Nasdaq: MSFT) is opening up is developer preview for Windows Phone 8.1.

According to the official website: Windows Phone Preview for Developers gives registered developers access to prerelease Windows Phone operating system updates for their development phone, directly from Microsoft ... The Preview program was created to give developers time to test their apps, and to validate that their apps run as expected on a real phone before an operating system update is made generally available to your customers.

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