All praise/credit goes here. I did make some changes, but only to the format and a few grammatical/spelling errors. This guide will show you how to restore your iPhone from 4.0 beta back to (a more stable) 3.1.3. This guide was made for the iPhone 3G, although there should be nothing stopping it working with a regular iPhone 3G. The original iPhone isn't supported by 4.0. Any mention of downloads are at the bottom of the quote.