Official Update (June 23, 2010): Official iOS 4 Jailbreak for iPhone 3GS, iPhone 3G and iPod Touch 2G from the iPhone Dev Team.
Update: There may be an iPhone 3.1.3 Jailbreaking method, you could learn How To Jailbreak iPhone 3.1.3 with Snowbreeze along with a tutorial video.
Update 2 (March 26, 2010): Geohot Untethered Jailbreak Tease.
George Hotz, also known as the famous Geohot hacker who has Jailbroken and Unlocked the original iPhone, then again provided the iPhone 3GS Jailbreak with Blackra1n and has started messing with the new PS3 Hack, has had some shattering news. According to Geohot, it seems that the new Apple iPhones that are running iPhone 3.1.3 OS cannot be jailbroken with Blackrain and may not be possible to Jailbreak at all. To add some extra salt on our wounds, he says that ‘there is no untethered jailbreak’*, which is some real depressing news.
Geohot has managed to provide Jailbreaking methods to previous iPhone models including the newest iPhone 3GS, yet the newest Apple iPhone’s firmeware consist of additional specs that are not allowing the regular Jailbreaks to happen. Moreover, although Blackra1n did in fact Jailbreak previous iPhone 3GS up to (and including) iPhone 3.1.2, this was still a tethered Jailbreak*. This meant that if you have Jailbroken the iPhone 3GS with Blackrain (and you were beyond certain RAM specs), then if the device is rebooted, turned off or restarted, you would HAVE TO connect it again and Jailbreak it once more for it to boot up and function properly.
Important iPhone Jailbreak Notes: For those that are itching for the new iPhone 3.1.3 OS (even though it doesn’t really add much), then the Dev Team may have found an iPhone 3.1.3 Jailbreak for the previous iPhone and iPod Touch models, using the Redsn0w 0.9 version (NOT INCLUDING iPhone 3GS and newest iPod Touch). You can find the instructions, warnings and steps straight at the Dev Team site.
If you run across real iPhone 3.1.3 Blackra1n Jailbreak info, an untethered Jailbreak or more updates from Geohot, then please share the news with the rest of us below.
*it is a tethered Jailbreak for certain iPhone 3GS models that are above a specific Boot Rom version. For those below, it is an untethered Jailbreak. Thanks Nick for the correction!