If you have some knowledge of Silverlight and .NET it will be so easy to leverage your knowledge and develop for WP7 codenamed Mango. Please see this new ad for Mango update: [youtube=http://www.youtube.com/watch?v=XpI8252TieM&feature=player_embedded]!
Disclaimer: The opinions expressed herein are my own personal opinions and do not represent my employer's view in any way.