You can create custom cooked iOS 4.3 firmware with PwnageTool or sn0wbreeze and  custom iOS 4.3 will jailbreak iOS 4. on iPhone 4,3GS. If you want to jailbreak iOS 4.3 without jailbreaking. I have made custom cooked iOS 4.3 firmware for all iDevices just for you. Mod Your Pod's official custom iOS 4.3 firmwares are created with sn0wbreeze and can be restored via iTunes (download links below). Download iOS 4.3 custom firmware restore jailbroken and activated for iPhone 4, iPhone 3GS (old bootrom and new bootrom).  The iOS 4.3 activated custom firmware will provide untethered jailbreak.

* iPhone 4

* iPhone 3GS

1) Download (all parts) of custom iOS 4.3 firmware (IPSW) for your iPhone (links below).

2) Join the splitted custom IPSW file by unpacking them :

          * Mac Users : Use BetterZip ( or what ever you want )

          * Windows Users : Use HJSplit ( or what ever you want)

3) Now, you will get a .IPSW custom firmware.

4) Put your iDevice into DFU Mode.

For DFU mode : Turn off your iDevice while still connected to your computer. Hold the home button and power button for 10 seconds, then release the power button.

5) Press the Shift key for Windows or ALT for Mac and click restore and use the custom IPSW.

6) It will restore your iPhone/iPod Touch and will jailbreak it.