Microsoft isn’t saying “Windows Phone 8.1″ on Monday at Mobile World Congress, but the company is detailing a few of its features. In an update arriving this spring, Microsoft’s Joe Belfiore says the company will “technically” support all existing Windows Phone 8 devices. It’s not clear whether carriers will allow Windows Phone 8.1 devices to upgrade, but Microsoft is announcing its own support of existing devices. That’s a change from the Windows Phone 7 to Windows Phone 8 release, where existing devices were able to upgrade to 7.5, but not to the latest 8.0 version. While Microsoft is only saying spring for this Windows Phone update, Belfiore also took some time to reveal some of the changes the company is working on. Microsoft will support on-screen buttons with Windows Phone 8.1, alongside new hardware support for Snapdragon 200, 400, and 400 LTE chipsets.