There's no doubt that Apple currently leads the appstore race, atleast in terms of numbers, but Microsoft seems to be determined to do everything they can to woo developers for their WP7 platform. They have announced an API mapping tool : iPhone/iOS to Windows Phone API mapping tool.
Announced on the Windows Phone Developer blog, the tool is described as a sort of translation dictionary for quickly porting snippets of iOS code to C# equivalents.
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.
For the current version, three types of APIs are supported : Network / Internet, User Interface and Data Management. Though they do not plan to provide mapping for all the APIs that iOS has, they do plan to improve and expand the scope in later versions.
Microsoft has also published a 90-page+ whitepaper titled "Windows Phone 7 Guide for iPhone Application Developers". Microsoft has also given devs an option to suggest which APIs they would like mapped and they have also begun a series of "developer stories" in which devs share their experiences and reason for porting apps to Windows Phone 7.
Microsoft is definitely following its "Developers! Developers! Developers!" motto and the upcoming Nokia-Microsoft dev engagement initiatives are only going to boost developer interest in Windows Phone. You can get the tool, whitepaper and other resources at the source link.
