The tethered jailbreak for iOs 4.3.1 is awailable for iPhone 4, and shall be made availablre for other devices like iPad and iTouch soon.
The followinf bundle can be used to jailbreak iPhone 4 with Pwanage Tool 4.2 (MAC only).
Here are the instructions :-
Requirements:-
Latest version of iTunes for MAC
Pwanage Tool 4.2
iOS 4.3.1
iPhone 4 (GSM)
iPhone 3GS
iPod touch 3G
iPod touch 4G
iPad
iPad 2 WiFi
iPad 2 GSM
iPad 2 CDMA
Custom Bundle for Pwange Tool 4.2
Thethered Boot Utility
RamDisk Fixer

Step 1 : Extract the custom bundle and copy the “ iPhone3,1_4.3.1_8G4.bundle ” file.

Step 2: Place the Pwanage Tool 4.2 downloaded earlier in “Application” folder and right click and select “Show Package Contents”.

Step 3: Browse to “browse to Contents/Resources/FirmwareBundles/” and paste the “ iPhone3,1_4.3.1_8G4.bundle ” file from Step 1.

Step 4: Now install the RamDisk Fixer pakage to enable the iOS 4.3.1 support on Pwanage Tool 4.2.

Step 5: Now run Pwanage Tool and select Expert Mode and mark iPhone.

Step 6: Now locate the iOS firmware 4.3.1 where it resides.

Step 7: After loading firmware, Choose “create custom iOS 4.3.1 GM IPSW.”

Step 8: After creating the ISPW, get iPhone in DFU mode by clicking on DFU icon and following the instructions.

Step 9: Launch iTunes select iPhone as device then click on “Restore” Button while pressing the “Alt” key on keyboard.

Wait for the installation to finish.

Step 11: Yayyyy, now you have a iPhone 4 on 4.3.1 Jailbroken.

But wait, the jailbreak is tethered only at this stage. So if you reboot you would have to go in Jailbreak Mode manually again.
Source:GizMee