Your iPhone is probably not at the same quality level as your other(s) photo camera(s). But since the arrival of the iPhone 3G-S it looks more and more like a cute small photo notepad. But you still had no option to extend its lens with lens converters of any kind.
This is corrected by Factron, a Japanese company offering a metal box on which you can attach accessories.
Surprising, but it may be useful to somebody..