Here's an iPhone feature that could have completely slipped your radar: zooming in and out of your screen.
The zoom feature, which can be turned on in the Settings menu, uses a three-finger tapping system to zoom in on any screen. Just double tap with three fingers to zoom. To move around when zoomed in, drag three fingers around the screen. And to change the zoom farther or closer, double-tap and drag three fingers up or down.
This feature only works with the iPhone 3GS and new iPod Touch, not older models. To activate the zoom feature, tap Settings, General, and then Accessibility.