Safe unlock strategy for 3GS? (4.1 with 05.12.01 and 05.13.04)

[jeff-4]

I am a newbie here, and this forum looks great!

Here is my question:

I recently purchased several iPhone 3GS's for my family. All are unlocked and working fine on the T-Mobile network, but I and would like to make them "identical" by bringing them all to iOS 4.1 while keeping their untethered jailbroken/unlocked status. (By the way, I wouldn't mind going to 4.2.1, but I do not want to replace the baseband with the iPad version -- in case, for some reason, I want to revert back to a "stock" AT&T phone.)

Before I risk screwing up my family's communication lines, I wanted to get some assurance that my plan will work.

First, here are the phones, all 3GS, with iOS, baseband, and jailbreak/unlock history indicated.

3.1.3
05.12.01
Jailbreakme and ultrasn0w

4.0.0
05.13.04
Jailbreakme and ultrasn0w

4.0.1
05.13.04
Jailbreakme and ultrasn0w

4.0.2
05.13.04
Limera1n and ultrasn0w

I believe that all have the new bootrom (I can find and post the exact numbers, if this info is needed). All have 4.1 SHSH blobs saved via TinyUmbrella.

Here is my plan. Use Pwnage tool (on my Mac) to update each to 4.1 while preserving the baseband, running TinyUmbrella server during the process to allow iTunes to install the customized 4.1 firmware. Then, via Cydia, unlock each with ultrasn0w.

WIll this work? Must I use only certain versions of Pwnage tool and ultrasn0w? Any other concerns? Much thanks to any comments!

[iYeow]

Everthing is correct except you don't use tiny umbrella when restoring to custom firmware of 4.1. Make sure you use the dfu from Pwnage tools or Redns0w to put you into DFU mode.

[mickish1953]

Take a look at the following link, should give you all the info you need.

[How To] Check if you can Unlock

Hope it helps.

[jeff-4]

Everthing is correct except you don't use tiny umbrella when restoring to custom firmware of 4.1. Make sure you use the dfu from Pwnage tools or Redns0w to put you into DFU mode.

I apologize for my ignorance, but since 4.2.1 came out (and Apple no longer signs for past firmware), won't there be an issue to install 4.1 (i.e., the customized 4.1) in iTunes? Does DFU mode put in the firmware without sending out the SHSH to Apple.

Thanks for helping me to understand!

Take a look at the following link, should give you all the info you need.

[How To] Check if you can Unlock

Hope it helps.

It is a very useful post, but I wanted to make sure that the baseband is preserved so that the unlock will work with 4.1. Although you do explicitly mention preserving the baseband, the tutorial listed for iPhone 3GS Pwnage Tool (Mac) does not say anything about it (which made me nervous).

Thanks again!