What's highest firmware and able to unlock?

[Dubro]

My phone is 3GS at 3.1.2 with new bootrom. I want to JB it and unlock it. So do I upgrade it to 4.01 and then use Jailbreakme.com?
Or is there a better way and higher firmware version? thanks

[iYeow]

You can restore to custom firmware of 4.1 created by Snowbreeze 2.1 or Pwnage tools 4.2.1. Use Redsn0w 0.9.6b6 to put you into dfu mode only then run itunes : shift + restore to CFW of 4.1 .
Make sure you have atleaast itunes 9.2.
While building CFW from Snowbreeze, use expert mode and uncheck activate my iphone.

[Dubro]

thanks, would that be an untethered JB? I don't want a tethered. Does firmware 4.1 have any big advantages over 4.01?

[iYeow]

4.1 only has an additional of gamecenter to play online. You can stay at 4.0.1 if you want.
Before doing anything and this is very important go download tiny umbrella , plug iphone in and click save shsh.
If you don't do this, then if you are stuck, TU will not be able to recognize your iphone and you do not have info in TU.

4.1 is untethered, just don't go to 4.2.1.

[Dubro]

OK I saved the shsh file. Now I just upgrade to 4.01 with iTunes then go to jailbreakme.com Correct?

[iYeow]

Do you see 4.0.1 shsh blob in TU ? If you see it then start Tss Server, and shift + restore to 4.0.1 ipsw.