The Dev Team reported that it is safe to update your iPhone to OS 3.0.1. After updating your iPhone to the latest 3.0.1 firmware, you can run the latest version of RedSn0w and point it to firmware 3.0.
Since the 3.0.1 doesn’t update the baseband, you will also be able to unlock your iPhone using UltraSn0w via Cydia (for iPhone 3G and 3GS), and you will also be able to run RedSn0w on your iPhone 2G to unlock it by following these steps.
My latest tutorial on how to jailbreak your iPhone using RedSn0w still works and I suggest you check it out if you’re not sure on how to update and jailbreak your iPhone.
Note that in order to jailbreak, you will have to update to 3.0.1 in iTunes first, which will remove all your jailbreak apps.