The very first thing you need to do when developing a Windows Phone app is to get an AppID. You need to be a registered Bing Developer to get one. Then you need to focus on design.
The best design is a simple one. This cannot be stressed enough. The design tool for the Windows Phone is called Metro. It uses XAML to layout your user interface.
There is a clear separation of your phone application logic and the user interface design. That is the way of XAML. Of course Visual Studio is the IDE of choice to develop your code in.
A Little Bit of Crypto - I have been trying to figure out to "collision resistant" some of these standard hash functions are. It is a tough concept to get my head around. I figure...