Microsoft is sending an email to developers warning about the dev unlock deadline - December 31, 2014 - for Windows Phone 7.x devices.Make sure to unlock yours before that date 
Source: Developers: You Will Not Be Able To Unlock Windows Phone 7.x Devices For App Testing Starting Dec 31st
Source: Developers: You Will Not Be Able To Unlock Windows Phone 7.x Devices For App Testing Starting Dec 31st
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