iPhone firmware 3.1 is out, here is a step by step guide to jailbreak iPhone 3.1 using  PwnageTool 3.1 courtesy the iPhone Developer blog.

1. If you are using a 3G iPhone with ultrasn0w and rely on ultrasn0w to obtain cellular service, then you should only upgrade to 3.1 with a PwnageTool created .ipsw. – Stay away from Apple’s direct updates as described here ^[1] and here ^[2] please get up to speed on the whole subject by reading the information contained in these posts.
2. If you have an original iPhone (1st generation) then 3.1 unlock works with this PwnageTool release. iPhone 3G users upgrading to 3.1 will need to continue using ultrasn0w with a PwnageTool created 3.1 .ipsw
3. Please read all parts of this post before downloading and using these tools.
4. Read items 1, 2 and 3 again and again.
5. Links to download PwanageTool 3.1 to Jailbreak iPhone 3.1 ^[3].
6. This app is suitable for the recent 3.1 release.
7. This version of PwnageTool will NOT work for the iPhone 3GS.
8. PwnageTool WILL work for Original iPhone (1st Generation), Original iPod touch ^[4] (1st Generation) and the iPhone 3G.

This does not support the 3GS or 2G/3G version of iPod touch ^[4]. The development team is also planning to release a new version or redsn0w for both Mac OS X and Windows shortly.

[3.fun ^[5]]