The Telerik UI for Windows 8 XAML cannot be used both for Windows Phone 8.1 and Windows 8.1(Universal App) but only in a Windows 8.1 project. Also the Telerik UI for Windows Phone 8 cannot be used in an Universal App but only in a Windows Phone 8.1 Silverlight project.
I suggest that you take a look at the following blog post : http://blogs.telerik.com/windowsphoneteam/posts/14-04-08/telerik-ready-for-microsoft-universal-windows-apps
that reveals our statement about the Universal Apps.
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