If you're going to be buying your first iPhone this week, you might want to add this to your bookmarks. Apple has posted an iPhone-formatted version of their iPhone 3G Users Guide that can be viewed directly in Mobile Safari, so you can always have it when you need it. It includes information on the Phone app, Mail, Safari, the iPod app, Applications in general, Settings, the Wi-Fi music store, and a few tips on troubleshooting.
Apple Linky
Source:
TUAW
EDIT: Im sorry to inform you but the link is now down

I don't know if it was moved or what but I'll fix it if I can find it.