GeoHot beat the iPhone Dev Team on this one, but no worries – It’s all good. You can create your own custom pre-jailbroken IPSW and restore it on your iPhone, iPhone 3G, iPhone 3GS, iPod Touch 1G, iPod Touch 2G but sadly, no iPod Touch 3G support, you’ll have to use GeoHot’s Blackra1n to jailbreak.

SUMMARY:

• The iPhone 3GS is now supported out of the box in PwnageTool 3.1.4 (or if you have upgraded to 3.1.x in iTunes)
• The iPod 2G is still supported in PwnageTool 3.1.4 but you must already be jailbroken (we’ll update this if there’s a big demand from non-jailbroken ipt2G owners)
• The iPod touch 3G is NOT supported

DETAILS:

• GOLDEN RULE: If you are using a iPhone 3G or iPhone 3G(S) with ultrasn0w and rely on ultrasn0w to obtain cellular service then you should only update your device with an .ipsw that is made with the new PwnageTool. There are no second chances with this. You need to remember that PwnageTool will provide an upgrade path to newer versions of the iPhone software in the future.
• Please read all parts of this post before downloading and using these tools.
• Read items 1, 2 and 3 again and again.
• PwnageTool will work for the iPhone 3GS
• PwnageTool will work for the iPod touch 2G
• PwnageTool WILL work for Original iPhone (1st Generation), the iPhone 3G and iPhone 3G(S) and the iPod touch (1st Generation and 2nd Generation) but NOT the iPod touch 3rd generation.
• For 3G and 3G(S) users who are Pwned, PwnageTool is your key to updating in the future, just remember to never install an update directly from Apple, always use an .ipsw that has been created with PwnageTool.
• There is no Windows version of PwnageTool it is a Mac OS X tool only, we are not developing a Windows version of PwnageTool.

Download:
PwnageTool 3.1.4 Download for Mac OS X

IPSW Downloads:
iPhone 3GS 3.1.2 ipsw Download
iPhone 2G EDGE 3.1.2 ipsw Download
iPhone 3G 3.1.2 ipsw Download

- source: blog.iphone-dev.org