A couple days ago, DevTeam released their newest jailbreaking tool (Redsn0w 0.9.6b4 with compatibility of cydia and mobile substrate with IOS 4.2.1) that can used to jailbreaking IOS 4.2.1.
First of all, i would like to say big thanks to devteam that make this jailbreak happen… you guys are awesome 😀
Please backup your data in your iphone before doing this jailbreak.
note #1 : If you are an unlockers or Iphone Software Unlock users, you should check Dev Team blog in here to make sure your iphone is jailbreakable (cause it will updated your iphone baseband to 05.15.04. If you accidentally updated your baseband, you need to wait for devteam to release new ultrasn0w to do unlock).
note #2 : after i jailbreak my iphone to ios 4.2.1 using this redsnow, i found some problems. When i switched running application from multitask bar, it always crash and respring.
note #3 : Qtweeter 3.6.4 doesn’t want to run in this IOS 4.2.1. Got no luck for this one.. 😦