The new iPhone OS 3.0.1 that fixes the SMS vulnerability that allowed hackers to gain control of your iPhone can be jailbroken using the same procedure as the previous 3.0 jailbreak. You do need to use the latest version of Redsn0w 0.8. I have updated all the download links to the new version.

After you have updated your iPhone to 3.0.1 you can follow these instructions exactly to jailbreak it.

OG iPhone
iPhone 3G
iPhone 3G[s]

When you come to the step where you browse for your firmware, you want to select the 3.0 firmware that you downloaded, even though you are running 3.0.1  This will trick Redsn0w into jailbreaking 3.0.1.

When you are done, you will be jailbroken running 3.0.1 and be totally safe from the SMS hack.