Microsoft launched today the API Mapping tool for iPhone. Basically, it's a utility that will look at the calls your iOS app's code is making and help you find a new home for them in .Net's ample libraries. Microsoft is also providing documentation to help with the porting,
With this tool, iPhone developers can grab their apps, pick out the iOS API calls, and quickly look up the equivalent classes, methods and notification..
events in WP7. A developer can search a given iOS API call and find the equivalent WP7 along with C# sample codes and API documentations for both platforms.
The code samples allow developers to quickly migrate short blobs of iOS code to the equivalent C# code. All WP7 API documentations are pulled in from the Silverlight, C# and XNA sources on MSDN.
What sort of applications does the mapping tool address?
Taking a step back, the iOS APIs can broadly be classified into the following categories: Audio / Video, Data Management, Graphics / Animation, Network / Internet, Performance, Security and User Interface
For current mapping, we started with 3 popular categories (Network / Internet, User Interface and Data Management) and mapped them to Windows Phone 7 API.

Source : Microsoft