While I don't have any experience on the subject, I did recently see an article about using HTML5 to make an offline compatible iPhone game: http://sixrevisions.com/web-development/html5-iphone-app/

And here's another article from IBM about offline web/mobile apps in a more general sense: http://www.ibm.com/developerworks/web/library/wa-offlineweb/...

Hopefully these can help you out in some way!