Nitobi has announced PhoneGap for Windows Phone 7, nicely timed just before the Microsoft BUILD conference next week.
After unpackaging the contents of the www folder, your www/index.html file is loaded into an embedded headless browser control. This is essentially the same paradigm as other platforms, except here it is an IE9 browser and not a webkit variant. IE9 is a much more standards-compliant browser than previous IEs, and implements commonly used html5 features like DOMContentLoaded events, addEventListener interfaces, and CSS3. Be sure to use to get the html5 implementation otherwise the browser may fallback to a compatibility mode, and your code will likely choke and die.
The version for Windows Phone 7, just released in preview, is extended to support features including the camera, accelerometer, contacts, and notifications. There is also support for plugins:
PhoneGap-WP7 maintains the plugability of other platforms via a command pattern, to allow developers to add functionality with minimal fuss, simply define your C# class in the WP7GapClassLib.PhoneGap.Commands namespace and derive your class from BaseCommand.
In general Windows Phone 7 is not well supported by cross-platform toolkits, so PhoneGap support is an interesting development. PhoneGap has a high profile currently, and is being integrated into a diverse range of tools ranging from Adobe Dreamweaver to Embarcadero RadPHP, as well as the standard PhoneGap tools based on Eclipse.