A. D.'s List: iPhone Human Interface Guidelines for Web Applications

Almost by definition, users use iPhone while they are mobile. Whether they’re in a car or a train, sitting in a cafe or on a park bench, taking a walk, shopping, or waiting for an appointment, users use iPhone in environments that are likely to be filled with distractions. This does not mean that your iPhone solution can’t or shouldn’t perform important tasks that require users to concentrate. But it does mean that you must be prepared for the probability that users will not be giving their undivided attention to your content, at least not for long.

it’s important to remember that iPhone users can change the scale of the viewport by zooming in and out, but not the size. The only exception to this is that when users change iPhone from portrait to landscape orientation, the viewport size changes.

iPhone users perform specific movements, called gestures, to get particular results.

It’s essential to keep in mind, for example, that instead of the layered windows, desktop, mouse, and file system with which you’re familiar, iPhone has a small, fixed screen size, a browser interface supplied by Safari on iPhone, a touch-based input system, and no accessible file system.