I created a question on GetSatisfaction which is the official support site for Autodesk Sketchbook. I put in a question for them to create a Sketchbook app for Windows Phone. It shouldn't be difficult since they have a WindowRT app. Please like it.
Here is the link.
http://gsfn.us/t/3yuzg
Here is the link.
http://gsfn.us/t/3yuzg