Here is a quick heads-up about the official iPhone 4 and iOS 4 user guide released by Apple. The 28-chapter, 244 page guide covers a host of iOS 4 features—including syncing and file sharing, all the core, pre-installed applications, iBooks, Nike + iPod functionality, and accessibility.
The book includes tips specific to the iPhone 4, but it also includes tips for the 3GS and 3G. When a section of the manual is only applicable to a certain device, it is noted at the beginning of the section.
If you’ve been using an iPhone for any length of time, you’ve probably figured out most of this stuff already. It’s a good resource for new users, though.
Download iPhone 4 & iOS 4 User Guide [PDF link]
Alternately, an iPhone-formatted version is available through Safari for iPhone.