we do not support this scenario. Our grid panel is not virtualized and that is why you get the slowdown. What I can recommend you, if it is possible for you, is to use a listbox with virtualized stack panel and make your own templates that can mimic the layout of a grid. For the moment this seems like the only solution for me.
BTW: I'm really interested in your scenario - what data are you displaying on the phone so that you have this requirement?
the Telerik team
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