The iPhone is pretty popular, but many feel that its camera is somewhat limited. There are several kits out there to add zoom or wide-angle to the phone, but mostly at unfriendly prices (much like the phone itself...). There is, however, an easy and cheap way to take close-up photos with the phone.
The simplest and cheapest way is to use any magnifying glass. Just get a 50 cents piece from an office or toy store and hold it in front of the phone's lens. This way, you can take reasonable sharp images at about 2 inches. Keep in mind, though, that a good picture requires light!
A big challenge in this scenario could be holding it together. You need one hand to hold the phone, another for the magnifier and a 3rd for pushing the shutter button. A good solution that is not too expensive is getting the Victorinox SwissCard Lite. These cost about 20 dollars, and can be very handy for a lot of things. The SwissCard Lite has a small magnifier at its corner, so it's very convenient to hold against the phone with one hand, freeing the other one for hitting the shutter.
This solution, BTW, can be used with pretty much every camera phone in existence, as most of them don't have Macro mode.
Another little helper is the Fast Tap Camera application, available on the App Store for 1$. This application deals with one of the primary problems of the phone - the small size of the shutter button. With this app, the entire screen is the shutter button, so you can take a picture of yourself or just shoot at weird angels without fondling around for the little button.