Great example! That's what I needed.
OOOPS, SOME PROBLEM
For the reasons I don't know, adding a reference to Layout.Toolkit prevents aplication from starting, i.e. I see only black screen instead of first page. This happens even when running your source file.
I have Windows Phone 7 CTP from April refresh and Silverlight Toolkit v3 from November 2009.
What is going on?