Google has announced Google Gears for Windows Mobile 5 and 6 devices.

Google Gears works in exactly the same way on a Windows Mobile 5 or
6 device as it does on a desktop PC. If you’ve already written an application
that uses Google Gears, your application will also work on a Windows Mobile
5 or 6 device. Except, of course, only within the limitations of that
device. This means you need to consider things such as small screen
and limited ability to input text as well as the limitations of the Document
Object Model and CSS APIs present on mobile devices.

If Google Gears is expanded to work on Safari (Desktop and iPhone), then Gears might provide an easier way to develop for an iPhone than even Apple’s own SDK.