If you are wondering whether you could have jailbreak your Iphone 4 with iOS 4.2.1 unthethered, you will be in luck! The Chronic Dev Team has relased the latest Greenpois0n for you guys to jailbreak it!
Head off to this link to check it out!
Please remember to read the instructions before proceeding with it. I am not responsible if you brick your iphone though!