Apple is due to push iOS 4 sometime today and as a word of advice, don’t update your devices as soon as you see iTunes prompt you about the new iOS. Allow developers to push stable jailbreaking tools. Also, DON’T update if unlock your iOS device. iOS 4 is confirmed to be unlockable , but the unlock is coming later this month.
If you really want to update and jailbreak right away, you can do that with beta and unofficial tools :
- iPhone 3G and iPod touch 2G (non-MC version) users can jailbreak with redsn0w 0.9.5b5-2 [Mac and Windows]
- iPhone 3Gs users can jailbreak with PwnageTool ( custom unofficial bundles )