We make a Windows Phone app called Proto Hound (I can't link it here due to the forum policies, but Proto Hound is in the Windows Phone Store) that you may be interested in. The app allows you to drag controls onto a canvas, customize everything and when ready, email the code (XAML) to yourself or somebody else. It's a very quick, easy way to create a functional prototype.
Our latest version is currently in review by Microsoft and should be published to the Store in a couple of days, if all goes well. That said, the current version of the app has a trial you can play with, so download that and let me know what you think.