PhoneGap, has now announced availability of a PhoneGap beta supporting Windows Phone Mango. On Windows Phone Mango PhoneGap leverages the new HTML5 support provided by IE9.
This new option to build applications targeting Windows Phone gives more choices to developers. In particular, Web developers will be able to easily leverage their HTML5 skills to target Windows Phone.
The beta version of the PhoneGap libraries can be downloaded from: https://github.com/phonegap/phonegap-wp7.
You can read more at the Windows Phone Developer Blog.