NEED HELP?iphone 3gs 3.1.3 to 4.2.1

[sallmin]

Hi to everyone.I am kind of novice I have iPhone 3gs 3.1.3 baseband 05.12.01 and I wanted to update it to 4.3 or 4.2.1 firmware but I never find how could this be done.If someone could tell me in details how to install 4.2.1 firmware on my iphone then unlock it and jailbreak it I would be very grateful.
THX

 

[Gregoris]

you would use pwnage tool or sn0wbreeze to create a custom firmware and hold off the baseband upgrade, then use ultrasn0w..

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