Redsn0w 0.9.7 has been updated to beta3 fixing more bugs related to non – GUI content which handles media content like Facetime, Winterboard themes, and embedded videos in iTunes. If you rely on the ultrasn0w carrier unlock, please do not use this updated redsn0w tool.
The official change log is:The third beta is now available (testers ONLY please!). This version extends the fix made in beta2 over to the non-GUI programs too (like the daemons that handle media content). That should cover things like Facetime, Winterboard themes, and embedded videos in iTunes.
Download the Redsn0w 0.9.7b3 for Mac OS from the source link given below and use the tutorial guide to untether jailbreak 4, iPod touch 4 or iPad running iOS 4.2.1.