Upgrade iOS 3.1.3 to 4.3.3 on Unlocked iPhone 3GS

Hello Experts--

I have a jailbroken, unlocked iPhone 3GS that i would like to upgrade from 3.1.3 to 4+ without messing up my unlock. Here's the phone specs:

- Baseband: 05.12.01
- SHSH blobs in Cydia: 4.1, 4.2.1r1, 4.3.3
- T-Mobile prepaid SIM (in US)

I've backed everything up on iTunes and using Tiny Umbrella. I've read quite a bit about the process online, and as I understand it I need to create a custom IPSW to preserve my baseband and thus the unlock (I'd like to avoid going the GPS-breaking iPad iOS route if possible). However, it appears the only way to make a custom IPSW is with Pwnage Tool on the Mac, and I have a PC.

So...I found this link online that includes detailed upgrade instructions as well as links to a pre-made custom IPSW. My questions to you: does this process look legit? Should I download a premade custom IPSW? Is there a more trustworthy source for a custom IPSW and/or instructions for upgrading my iOS?

http://techdeville.com/2011/05/22/how-to-update-to-4-3-3-on-3gs4-without-upgrading-baseband-custom-firmware-bundles-included/

Thank you!
LVL 7
G-WarrenAsked:
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andytagonistCommented:
Wow...you're in a tough place.
Let me lead off with this:  if Apple replaces your phone via AppleCare or warranty, it will most likely come with 4.3.3.

Next up:  if you unlocked on 3.1.3, that MIGHT have altered your baseband and disabled it from being upgraded at all.  If I remember correctly, baseband 6.xx.xx is not going to upgraded. If that's the case, you're done.

Continuing on:  I'm about 90% positive you will not be able to roll up to 4.3.3 since you probably do not have the signed SHSH blobs for 4.3.3 and you're NOT going to get them anymore.

My suggestion to you:  if you have an unlocked phone with 3.1.3 on it, you've had it for quite a while. You can either consider becoming somewhat legit or just live with what you have. I know you might have reasons for being with T-mobile, and the iPhone is just a far superior product than whatever else is around, but you're being forced to use software that was severely outdated over a year ago and you're anchored to one specific device.
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ishcabittleCommented:
Technically yes, the linked guide will upgrade your 3GS to 4.3.3 while preserving your baseband.  The real question is whether or not we trust TechDeville, and while the site absolutely looks reputable, you'd be hard pressed to determine if there is anything malicious in the pre made ipsw provided.

The alternates include asking a friend with a Mac for help, going to the community for ipsw sources (hackint0sh.org comes to mind), or simply staying at 3.1.3.

If it were me, I would go for the TechDeville guide with the knowledge that I could lock my phone and I would then need a backup plan.  My advice, however, is to find a Mac that you can use for 20 minutes and use Pwnage Tool to build the ipsw yourself.
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G-WarrenAuthor Commented:
Thank you for the advice!
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