Microsoft isnt saying Windows Phone 8.1 today at Mobile World Congress, but the company is detailing a few of its features. In an update arriving this spring, Microsofts Joe Belfiore says the company will technically support all existing Windows Phone 8 devices. Its not clear whether carriers will allow Windows Phone 8.1 devices to upgrade, but Microsoft is announcing its own support of existing devices. Thats a change from the Windows Phone 7 to Windows Phone 8 release, where existing devices were not able to upgrade to the latest version.