UPDATE: Apple released iOS 6.0.1, so you can NOT restore to earlier firmware (both original and custom), unless you have saved your SHSH keys. If you are on iOS 6.0 right now you can use this tutorial.
This is step-by-step instructions on how to perform tethered jailbreak of youriPhone 4 on iOS 6 firmware using RedSn0w 0.9.15 for Windows.
Tethered jailbreak means that each time you restart your device you will need to connect it to a computer and run redsn0w.
Take a look at the video from RedmondPie of the Chronic Dev-Team announcing Absinthe 2.0 at HITB:
For those who didn't follow the conference, or get caught up in the excitement that surrounded it, the 'one more thing' bomb-shell was related to the fact that the Dream Team used their presence at the security event to officially introduce the world to the v2.0 release of their one-click Absinthe jailbreak solution. After months of hard work and exploit finding, mixed with weeks of will-they-won't-they speculation, it turns out that they indeed did introduce us to Absinthe 2.0.
Our instructions how to jailbreak your device using Absinthe are available here.
Just like version 2.9.4 the new 2.9.5 version supports untethered jailbreak of A4 devices on iOS 5.1.1. Sn0wbreeze can be used to create a custom firmware with jailbreak and preserve iPhone modem (baseband) version for unlock.
Sn0wbreeze 2.9.5 supports iPhone 3GS, iPhone 4, iPad 1, iPod Touch 3G, iPod Touch 4G and Apple TV 2G. It does not work with A5 devices, like iPad 2, iPad 3 and iPhone 4S.
Using this tutorial you will be able to create a custom firmware, untether jailbreak and unlock iOS 5.1.1 running on iPhone 3GS. This tutorial uses Sn0wBreeze 2.9.5 for Windows.
Sn0wBreeze will also preserve baseband version if you need carrier unlock. It can also update your modem version to 06.15 if you need unlock and stuck with 05.14 or higher baseband. If you have new iPhone 3GS that was made after 28 week of 2011 upgrading modem will not help to unlock.
Chronic Dev Team released an update to untethered iOS 5.1.1 jailbreak utility - Absinthe 2.0.2. New version supports the latest iOS 5.1.1 9B208 firmware for iPhone 4 GSM. If you experience problems with previous versions - try 2.0.2
FireCore has announced an update to Seas0nPass that provides an untethered jailbreak for the latest 5.0.1 (5.1.1) firmware for the Apple TV 2G. Unfortunately Seas0nPass is not yet compatible with the new ATV3.
Don't Forget to Save Your iOS 5.1.1 SHSH Blobs to preserve the ability to do iOS 5.1.1 untethered jailbreak in the future. Apple might release updated iOS firmware soon to fix and disable the jailbreak. After next firmware release you will not be able to restore to 5.1.1 any more.