Documentation and the iPhone Simulator "Documentation: none," proclaimed Peter-Paul Koch when he started playing with Safari for iPhone--but the situation has changed since then. Apple now makes iPhone-specific web development information available as part of the Safari documentation.
The iPhone SDK (software development kit), which is Mac-only, also contains an iPhone simulator--this is very handy if you already own an iPhone, and of course it's absolutely essential if you're yet to join the iPhone army. To access it, you'll need to register as an iPhone developer, and install the iPhone SDK. Once you've installed it, you'll find the iPhone simulator in /Developer/Platforms/iPhoneSimulator.platform/Developer/Applications