I have a jailbroken unlocked iphone 3GS with iOS 4.0.1 and baseband 05.13.04. I am wondering if it is possible to upgrade to a newer iOS and keep my unlockable baseband so that I can stay on tmobile...any assistance would be greatly appreciated . Thank you for your time
You can upgrade to 5.1 with a custom ipsw to preserve your baseband, if you want to update to anything lower than that, you'd need an old bootrom 3GS. Also, note that 5.1 is a tethered jailbreak and ultrasn0w requires an external fix to work.
answered 13 Apr '12, 12:38
is it possible to upgrade to 5.0 while still keeping my unlock or re unlocking it?
answered 13 Apr '12, 14:48
Tutorial for updating iPhone 3GS whilst preserving baseband for unlocking:
There are two bootrom versions of the iPhone 3GS. They are old (359.3) and new (359.3.2). It is best to confirm by actually checking the bootrom version however the Serial Number or Manufacture Date of the board is a good indicator. All boards manufactured prior to the 40th week of 2009 are old bootrom. From week 40-45 is a cusp period where either version may have been used. Also remanufactured iPhones indicated with a serial beginning with 5K or QR may have recycled an old bootrom chip.
Old bootrom will always be untethered jailbreak based upon the exploit used. Old bootrom also does not require the SHSH blobs to restore to any given iOS version.
New bootrom requires an untethered jailbreak to be released for the given iOS version. New bootrom requires SHSH blobs to restore to any version of iOS that is not currently signed by Apple.
Here is a general guide for updating or restoring a new bootrom 3GS outside of the signing period:
You can grab what you need from here: JailbreakQA Links
Please post in comments if you have further questions regarding the procedure for your situation. For most accurate advice, please access the Settings App on your device and provide from General>About the Model, Version, Carrier, Serial (first five digits), and Modem Firmware. This info can also be accessed using Tiny Umbrella.
Your info will look something like this:
Model: MC131B Carrier: O2 UK Version: 4.3.3 Serial: 88935xxxxxx Modem Firmware: 5.11.07
Hope this helps, best wishes and good luck!