How do you unlock ATT 3GS - v4.2.1?

[Chiuy]

Hi guys!
My friend recently lost her phone and I want to give her my old 3GS for a temporary use. The problem is that the phone is ATT while she is on T-Mobile. So, I was wondering how you get the 3GS that is running on 4.2.1. to unlock?
It is jailbroken but I'm not sure with which program, maybe pois0n... something?
Any help will be appreciate to format the phone, unlock it, jailbroken, and to the newest version possible.
Thanks!

[Baggio]

Originally Posted by Chiuy

Hi guys!
My friend recently lost her phone and I want to give her my old 3GS for a temporary use. The problem is that the phone is ATT while she is on T-Mobile. So, I was wondering how you get the 3GS that is running on 4.2.1. to unlock?
It is jailbroken but I'm not sure with which program, maybe pois0n... something?
Any help will be appreciate to format the phone, unlock it, jailbroken, and to the newest version possible.
Thanks!

Buy a AT&T IMEI unlock code on eBay. It will cost about $5 and will take about 24 hours to go through. The phone will then be factory unlocked and can be updated without worry of losing the unlock. If that phone is yours and you have an account with AT&T, they will unlock it for free as long as that phone isn't under contract.

[Chiuy]

Is there a way to manually unlock it yourself?

[Baggio]

Originally Posted by Chiuy

Is there a way to manually unlock it yourself?

Ultrasn0w via Cydia if you baseband is compatible.

[corys00]

Originally Posted by Chiuy

Is there a way to manually unlock it yourself?

If it's your old iPhone, you can call AT&T and request them to unlock it at no charge.