iPhone and iPhone 3G camera has fixed focus lens (but not iPhone 3GS) and the image get blurred if the object is closer than 9 inches.
Here are some tips to get better quality pages:
• If you use iPhone or iPhone 3G, hold the iPhone at least 9 inches away from the paper.
• Make sure the page is flat.
• Ensure that the page is well lit without shadows.
• If the text is still too faint, try maxing out the contrast in grayscale mode.