Do NOT try to restore to 3.1.3 it restores, and then goes into recovery mode. It isn't possible to downgrade, I just tried. If you attempt a downgrade it will go into recovery and from there you will have to restore to the iphone os 4 gm again. I'm pretty sure we will be able to plug our phones in on the 21st like any other iphone user and receive the update. While I do not know this for sure, I'm am pretty certain, due to the fact that itunes will not allow you to downgrade. At any rate, here's a similier thread I created about the topic. Hope I helped! If I did, could you please tip the scales! Thanks!
Originally Posted by Cjchase95