To be honest I am not really sure how an Apache server handles the requests and which are the additional steps you must perform to make crossdomain calls work. Since it is a more general question, I'd advice you to post it in either on Silverlight.NET forums or stackoverflow. Meanwhile, if you permit, it would be great if we turn this support ticket to a forum thread since there might be a member of the Telerik community who has knowledge on the subject.
the Telerik team
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