iPhone 3GS 3.1.3 to iOS4

[dotFIVE]

I just bought an iPhone 3GS off of Craigslist. It's on 3.1.3 with 5.12.01 firmware. Jailbroken and unlocked. I think it has an old bootrom because the model is MB and the 4th and 5th numbers in the serial are less than 40.

I asked the guy how it was jailbroken and he said it was done through jailbreakme.

I tried to download the SHSH's off of TinyUmbrella but I only got 4.1 so I guess that's all it has.

How would I go about upgrading to iOS4? Since it's an old bootrom, it can accept custom firmware, right? I want to up to iOS4 without upgrading my baseband. Any version will work for me, as long as I can still keep my unlock. I'm also on a Mac.

How would I do this?

[iYeow]

Cool, I remembered you asked the question on how to choose a 3GS.
Yes, you can use Custom firmware, install jbme2pwn and reboot your iphone.
Now build your custom firmware from Snowbreeze 2.0.2 and uncheck the activate my iphone.
Build it and it will be placed on your desktop and named Snowbreeze_4.1.ipsw
Put your iphone into Recovery mode.
Do the Shift + Restore to Snowbreeze_4.1.ipsw
Put your sim card to activate
Now you are jailbroken at 4.1
Install Ultrasn0w to unlock.

Make sure you update your itunes to the latest.
Enjoy..

Since you only have 4.1 shsh blogs, as long as you stay away from Stock firmware and if you ever want to do a restore, just put iphone into recovery mode and restore to custom firmware again.

[dotFIVE]

Thanks for the help.

The repo for jbme2pwn is currently down. I get a 404 Not Found error when I try to download it. Any other suggestions?

[eyeRobot]

You need to wait for it to come back, it's been down a few days.

You must double check what it's JB with or you are running the risk of messing the phone up. When you boot the phone up and the apple logo appears, does a line of pixels along the top right edge also appear? If so, it's going to be jailbreakme. If not, then I would suggest it's JB with spirit and you need spirit2pwn.

Also, it's all well and good the 4th and 5th numbers being below 40, but the 3rd number would have to be a 9 too. You should double check your bootrom with instructions from this link:

How to Check iPhone 3GS New Bootrom / Old Bootrom (iBoot) Version | Redmond Pie

[dotFIVE]

Ooh, you're right. Unfortunately I have a new bootrom. Thanks for saving me from a bricked phone though!

So.. pretty much I have to wait until a new unlock is released before I can update to iOS4?

[bellyfrog]

The numbers can't always be trusted. Download iDetector from iH8sn0w.com | Jailbreak your iPod touches and iPhones and that will detect the bootrom for you.

[eyeRobot]

Yes, no way to get to 4.x if you require an unlock.

Keep an eye out for Pwnagetool which is supposed to be released today. It should work on new bootrom.