Recently I have been thinking of different ways you could store simple text messages and the like on an iPhone. There are a number of note applications out there and you can sync the iPhone note application with some e-mail clients.
Anyway, I ran across this inventive solution, store an entire application in a URL. Its all explained on the Life with Lunchhooks blog. Now that is really cool. Simply put that in a link. Then click the link and save it to your Bookmark list. Whamo-bamo, you have some offline data stored on your iPhone. The only limitation is the data is read only.
But fear not, there are a number of ways you can store applications that can both read and write offline. Apple has this offline application programming guide on their web site. Really neat stuff. I gotta find some time to play with this. :)