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Previously released Windows Phone hardware is incapable of being upgraded to Windows Phone 8, due to changes in the kernel requirements and hardware specifications. However, Microsoft announced at the Windows Phone 8 announcement event that Windows Phone 7.x devices would receive a free upgrade to Windows Phone 7.8. Microsoft announced Windows Phone 7.8 alongside Windows Phone 8 and began pushing the update to devices in January 2013. It added some features from the Windows NT based Windows Phone 8, backported to Windows Phone 7. These features included the updated start screen that allowed users to resize live tiles, additional theme colors, and an update to the lock screen that would optionally display the daily Bing homepage picture automatically. Windows Phone 7.8 does not support USSD.