Microsoft is sending out emails to Windows Phone app developers informing them that they will no longer be able to unlock any Windows Phone 7.x devices, like the Lumia 900, for app testing after December 31.



From Windows Central:

Microsoft recommends that app developers who want to unlock those phones do so before the deadline so they can continued to be used for app testing for another 24 months. The email added:

"After December 31, 2014, no Windows Phone 7.x unlock capabilities will be available. This means, for those of you who have not unlocked your Windows Phone 7.x device, testing of apps directly from Visual Studio on that device will no longer be possible. However, app testing can still be done on other unlocked phones, or via the Windows Phone Emulator, or by submitting beta apps through the Windows Dev Center."

  Microsoft ends unlocking of Windows Phone 7.x devices for developers Dec. 31