Apple’s freshly released iOS 4 added a new digital zoom feature that’s compatible with the iPhone 3G and 3GS Camera app.
To use the digital zoom feature, launch the Camera app, and then tap on the view finder area to show the zoom slider. Sliding your finger to the right zooms in, and sliding to the left zooms out.
iOS 4’s digital zoom slider
Since the zoom feature is digital, the final image won’t look as good as if you used an actual zoom lens. It will, however, work in a pinch and since it’s included with the free iOS 4 update, it won’t cost anything extra to try it out.