Depends on your goal. However, the big issue there is the UI is different on all platforms. You still have redo all that. Java has tried the "Write once, debug everywhere" thing before. I have yet to see a compelling UI in a Java application.

>There is a bunch of stuff out that lets you write your app once then compile it for WP, Android, and iOS - phonegap is one of them - seems to me that doing something like this would be the way to go?