If its already jailbroken then use redsnow and just tick upgrade baseband and it will do the rest for you ie upgrade bb to 06.15 , then you can use ultrasnow 1.2 to unlock .
You must also download the iphone 3gs 4.2.1 firmware and put it in the same folder as redsnow and select it when asked. There are videos on youtube as well . Hope this helps
You must also download the iphone 3gs 4.2.1 firmware and put it in the same folder as redsnow and select it when asked. There are videos on youtube as well . Hope this helps