I wouldn't downgrade Im on a 3G and if your going to restore anyways just jailbreak. Even if you don't want anything from cydia, if your thinking about selling your 3G, you can unlock it and it looks really good that you have firmware 3.1.2. Plus when you downgrade, aggie is talking about installing a benm tether hack or modifield config file which disables MMS, visual voicemail and in rare cases you can't connect to the Internet. With the sinfuliphone you just install and restart and everything is readily available. And downgrading is pretty difficult as well.