Currently we cannot give an exact estimation whether we are going to implement such functionality. In fact, there is a built-int spell checker on Windows Phone 7 which does the job pretty good. You can give it a try.
Do not hesitate to get back to us in case you have further questions or need assistance.
All the best,
the Telerik team
Let us know about your Windows Phone 7 application built with RadControls and we will help you promote it. Learn more>>