While GeoHot has already released his jailbreaking tools called Purplera1n for the iPhone 3GS on both Windows and Mac platforms, the iPhone Dev-Team followed suit today with an updated Redsn0w 0.8 after initially announcing that they will wait for the iPhone firmware 3.1. This Redsn0w 0.8 release can jailbreak the iPhone 2G, 3G and 3GS, and both the iPod Touch 1st and 2nd Gen, plus support for Winterboard. It is availbale for Windows, Mac OS X, and Linux operating systems. The Ultrasn0w unlocking tool has also been updated to version 0.8 to support the iPhone 3GS.
Download Redsn0w 0.8 for Windows, Mac, or Linux.
After unlocking your iPhone 3GS with Ultrasn0w, reset your network setting once from your iPhone’s Settings->General->Reset->Reset Network settings.
You can then update your MobileSubstrate and Winterboard in Cydia.