Help with jailbreaking and Cydia for iPhones, iPads, and iPod touches.

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.

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:

1. verify you have your SHSH blobs for 5.0.1 and save them locally, you can do this with the Fetch feature in redsn0w.
2. build a custom no baseband 5.0.1 ipsw in redsn0w.
3. stitch your 5.0.1 SHSH blobs to your custom no bb ipsw.
4. enter pwn'd dfu using redsn0w.
5. shift (option mac) restore in iTunes and select your custom stitched no bb ipsw.
6. Activate with original carrier SIM card.
7. jailbreak as needed using redsn0w.
8. unlock if needed using ultrasn0w from Cydia.

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!