3GS with 3.1.2
I have iPhone 3GS with 3.1.2 (Old bootroom) Baseband 05.11.07.
already jailbreaken & Unlocked using blackra1n.
I want to uprade to 4.2.1? is it possible what is the best solution?
I have created custom firmware 4.2.1 on OS X & when i tried to restore in PC in DFU mode I get 1600 error message.
when i tried to restore in PC in recoery mode i got 21 error message.
You need to first put the iPhone into Pwned DFU mode - you can do this with redsn0w 0.9.6b4 or higher.
It is *NOT* enough that your iPhone was pwned already by blackra1n.
Then restore custom IPSW with iTunes.
Also, be aware that the custom IPSW made with this unofficial iPhone dev team bundle http://iphwn.org/advanced/iPhone2,1_...48a.bundle.zip will not give you a fully jailbroken 4.2.1 on your 3GS. It just prevents your baseband from being updated.
After you restore this custom IPSW, you still need to use redsn0w 0.9.6b4 up to 0.9.6 release candidate 8 to jailbreak - be sure to specify that you have an old bootrom 3GS when you jailbreak with redsn0w.
Thnaks for your reply.
I have updated sucessfully 3GS from 3.1.2 to 4.2.1 as per your advice without upgrading Baseband 05.11.07.
Thanks for your support.