Like most phone cameras, the iPhone's lens is focused for the most general possible use, i.e. nearly at infinity. TUAW reader Daniel Forsythe modded his iPhone to focus a bit closer up so he could use it to read bar codes that he shoots from magazines and equipment labels.
The mod involves breaking the glue that holds in the camera module and rotating the lens to bring the focus closer to the camera. With this hack, he can snap photos of close-in subjects. Check out his Flickr photo set for samples and discussion.
He writes that he plans to make a full mod guide should readers express interest in it. The photo seen here is focused to 0.25".