defor from Eastrain has posted an interesting DIY to make your iPhone 3G close-focus. It would require opening the phone itself, and so as you may very well expect, it will void your warranty.

There are about five steps to the process, most of which involve taking out the right screws and cables to get to the phone's camera. Essentially, the whole exercise culminates with the removal of the glue that the manufacturers have put in between the inner lens assembly and the outer body.

For the complete step-by-step process, follow the source link below. It will lead you to defor's how-to post.