3GS 3.1.3 w/5.12.01 unlocked to 4.?

[jlp16au]

I have a 3gs that is jailbroken and unlocked. It is running version 3.1.3 and firmware 5.12.01.

Which version of iOS4 should I be able to upgrade to and still keep my jailbreak and unlock?

Also what is the best way to accomplish this?

 

[Myzhi]

Upgrade using a custom firmware file (one that keeps your current baseband = possible unlock). Depending on what old SHSH files saved you have saved, if any, you can upgrade to that firmware. If you have no SHSH files saved, you can only upgrade to 4.2.1 custom firmware.

 

[jlp16au]

I don't have any SHSH files saved. Can I create a custom FW that will keep my old baseband and upgrade to 4.2.1?

If so, is there a way to do this using windows?

 

[Myzhi]

I don't have any SHSH files saved. Can I create a custom FW that will keep my old baseband and upgrade to 4.2.1?

If so, is there a way to do this using windows?

Pwnagetool is what you use to create custom firmware files, but that only runs on a Mac. Instead, you will have to find (google) for one (keeps your current baseband). Make sure, it's from a trusted site. After you get one, you must use Redsnow to put the phone into a special DFU mode, and then, restore through itunes with the custom firmware file.

Please note: If you have old bootrom, it will be a untethered JB. New bootrom would be a tethered JB.

 

[jlp16au]

I have a mac also, it is just not with me right now. How do you determine what baseband you have?

 

[Myzhi]

I have a mac also, it is just not with me right now. How do you determine what baseband you have?

On the iPhone, settings > general > about. Look at modern firmware (baseband).