Redsnow is easy to use, it is available for Windows and Mac OS. Pwnagetool can be used to create custom ipsw and preserve baseband, it supports Mac OS only.
Ultrasn0w doesn’t work on iOS 4.3.1 yet (even with iOS 4.3.1 + old baseband). The fix will be available soon. Here’s a warning from DevTeam for unlockers:
Good news everyone. DevTeam recently posted a tweet where they inform us that they will soon release a new version of Redsn0w utility for Windows. It will be an untethered jailbreak for iOS 4.2.1 using the Monte iOS 4.1 technique.
In fact, Apple still provides 4.1 ipsw and this could be used to jailbreak.
In addition, the team warns that Windows version will be very slow because the program uses the filesystem instead of RAM.
DevTeam worked hard for the last several hours and released jailbreak tool for iOS 4.2.1. It is redsn0w 0.9.6 b4.
As usual we remind all ultrasn0w unlockers please stay away from this official firmware. Wait for the ability to create custom 4.2.1 IPSWs that don’t update your baseband!
New redsn0w 0.9.6 b4 uses limera1n exploit and will successfully jailbreak all devices. The only problem is that it is a tethered jailbreak, which means you will have to plug it to a computer and rerun redsn0w on every reboot. This so called tethered or semi-tethered jailbreak. This condition applies to iPhone 3GS (new bootrom), iPhone 4, iPad, iPod touch 2G (MC model), iPod touch 3G and iPod touch 4G. Hackers are working hard to create untethered jailbreak for these devices. To use future untethered jailbreak you need to save SHSH keys for iOS 4.1 using TinyUmbrella utility or directly in Cydia.
Old devices like iPhone 3GS (old bootrom), iPhone 3G and iPod touch 2G (non-MC model) can be jailbroken-untethered right now using this latest version of RedSn0w.
Sn0wBreeze 2.9.6(pwnagetool for windows, supports untethered jailbreak of iOS 5.1.1 for iPhone 4, iPhone 3GS, iPod Touch 3G, iPod Touch 4G, iPad and Apple TV 2G)
Sn0wBreeze 2.9.3(pwnagetool for windows, supports tethered jailbreak of iOS 5.1 for iPhone 4, iPhone 3GS, iPod Touch 3G, iPod Touch 4G, iPad; untethered for iPhone 3GS with old bootrom; untethered for iOS 5.0.1, iOS 4, iOS 3 supports Apple TV 2G)
Sn0wBreeze 2.8b11(pwnagetool for windows, supports iOS 5, iOS 5.0.1, tethered jailbreak for iPhone 4, iPhone 3GS, iPod Touch 3G, iPod Touch 4G, iPad, Apple TV 2G; untethered for iPhone 3GS with old bootrom)
Current version is ultrasn0w 1.2.3, download in Cydia (unlock for iPhone 4, iPhone 3GS, iPhone 3G, firmwares 3.0-4.3.3; it supports basebands 01.59.00, 04.26.08, 05.11.07, 05.12.01, 05.13.04, 06.15.00)