And here is how apps can be written for Windows Phone 7:
Windows Phone 7 Series promises to be an amazing mobile phone operating system given its innovative user interface and functionality, as well as its great development platform upon which you can quickly and easily build games and applications. With a myriad of new devices, a powerful and immersive software platform, and a new marketplace to attract developers and provide easy access to applications, consumer demand for Windows Phones will be high, and developers will quickly adopt the Windows Phone platform to capitalize on this growing mobile marketplace. This Training Kit will give you a jumpstart into the new Windows Phone world by providing you with a step-by-step explanation of the tools to use and some key concepts for programming Windows Phones.
Check this training kit on Channel9.