I jailbroke my 3G running 4.0.2 with redsnow. I used this guide on youtube if you want to look at that.
[ame=http://www.youtube.com/watch?v=soklMMgnumk]YouTube - How To Jailbreak 4.0/4.0.1/4.0.2 - iPhone 3G, iPod Touch 2G[/ame]
Downloaded the 4.0 firmware to use with redsnow. Followed the instructions. Jailbroke perfectly but I can't get data to work on any apps/safari. I rebooted the phone and tried rejailbreaking with the same method and still won't get data. please help