The iPhone Dev Team, the geniuses behind all the unlocking and jailbreaking we iPhone users have been taking advantage of for years, have announced today that the new iPhone 3GS is indeed capable of being both jailbroken and unlocked. According to the Dev Team, the iPhone 3GS has no specific changes that would alter its ability to be jailbroken or unlocked.
Apparently, 24KPwn (the same exploit used to crack into the iPod Touch 2G) is applicable to the bootrom of the iPhone 3GS.
This means that you will be able to jailbreak the iPhone 3GS with redsn0w, and unlock it with ultrasn0w. However, the Dev Team claims that there are still some challenges presented by the 3GS, and they will need some time to work out the kinks to ensure the safety of the process.
So if you're dying to jailbreak or unlock the new iPhone 3GS, just hold on. You'll be able to very soon.
Important: If you are planning on jailbreaking/unlocking the iPhone 3GS, do not update with any new little firmware updates that Apple may release (the Dev Team is almost ready for this specific version.)