What are the gotchas of RE-jailbreaking/unlocking iPhone 3G?

[nsellen]

Hello. I've tried to read up on this issue so much that I'm dizzy. I'm hoping someone has the patience to help.

I have an iPhone 3G that had a service contract with AT&T in the U.S.

When I moved to China, I jailbroke/unlocked the phone myself and got a sim card and service from China Unicom. But over the last nine months, the iPhone's functionality has degraded: apps quit unexpectedly, Cydia doesn't work anymore (quits on launch), iTunes plays erratically, SMS doesn't present, phone reboots at will, etc.

So instead of a first-time jailbreak/unlock, I need my iPhone to be RE-jailbroken/unlocked. I'm at OS 4.0.2, which I've read may be part of the problem.

What are the gotchas of doing a clean jailbreak/unlock of my iPhone in its current bad state and that will allow me to continue using my China Unicom sim card?

For example, can I simply reset my iPhone via iTunes and start over using the instructions posted here? And should I remove my sim card when I do all of the procedures, or can I leave it inserted?

Thank you (profusely!) in advance for your help.

 

[Sine Qua Non]

You will need to create a custom IPSW with pwnagetool to prevent your unlockable baseband from being upgraded. Then, upgrade to that custom IPSW.

 

[eastercat]

If you're willing to go back to 3.1.3, that's probably the best software for the 3G. You can downgrade a 3G's ios without worrying about blobs, etc. Obviously, you'll be able to jb/unlock as well.
Going up to a newer ios requires use of custom ios in order to keep your unlockable bb. I suggest pwnage if you have a mac. Otherwise, you're stuck with the craptacular snowbreeze.

 

[nsellen]

If you're willing to go back to 3.1.3, that's probably the best software for the 3G. You can downgrade a 3G's ios without worrying about blobs, etc. Obviously, you'll be able to jb/unlock as well.
Going up to a newer ios requires use of custom ios in order to keep your unlockable bb. I suggest pwnage if you have a mac. Otherwise, you're stuck with the craptacular snowbreeze.

yes, i'm willing to go back to 3.1.3, so that sounds like a plan.

but forgive me - i'm not as tech-savvy as some of you. i still need to know:

1. can/should/must i do this downgrade through itunes? and,
2. should/must i remove my chinese sim card, and at what point - the beginning of the process?

thanks again. what a relief to get some answers!

 

[awadeee]

yes, i'm willing to go back to 3.1.3, so that sounds like a plan.

but forgive me - i'm not as tech-savvy as some of you. i still need to know:

1. can/should/must i do this downgrade through itunes? and,
2. should/must i remove my chinese sim card, and at what point - the beginning of the process?

thanks again. what a relief to get some answers!

1. If you want to downgrade, all you have to do is download the 3.1.3 firmware file from http://www.felixbruns.de/iPod/firmware/ , and then put your phone in DFU mode, and click shift + restore (Option + restore on a Mac) and select the firmware file and iTunes will restore you to it. There are many YouTube tutorials on how to enter DFU mode.

2. I don't think it matters a ton but I would take it out until after you are unlocked.

 

[eastercat]

If you can get an inactive AT&T sim off eBay, that's the best choice to have in your phone. This way, no need to hacktivate your phone.
Awadeee's advice on installation is spot on. When your mouse pointer is over the d/l link for the iOS, make sure it points to apple's servers. You never know when a malicious person could redirect the links to malware.