We’ve already gone over methods for downgrading an iPhone from iOS 4.0.2 to 4.0.1. Unfortunately, this method requires you to have your SHSH blobs on file on Saurik’s server, which some of you don’t have.
There is a post today on the Big Boss blog about how to downgrade from 4.0.2 to 4.0.1 without SHSH blobs, so I thought it might be helful to some of you.
I haven’t tried this myself and I can’t verify if this works or not but I’ve seen this method spreading on the web and it seems some people are successful at downgrading without SHSH.
This method works because of the similarities between iOS 4.0.2 and 4.0.1. So even if this works for these specific firmwares, it would not work for downgrading from 4.0.2 to 3.1.3 for example.
Go over the Big Boss blog to see the step by step tutorial, and tell us how it works for you.