I think i already know the question to this question, but it's worth asking. I upgrading my 3GS to OS 4 last week, but it was too unstable and i eventually downgraded back to my jail broken 3.1.2 (my files were saved on the shsh). My baseband is still os 4 though. It seems to be hurting my battery life. Additionally, i wanted to sell it unlocked to a friend soon. Now that my baseband is upgraded, is that impossible until they release an os 4 update now? And is downgrading it impossible?