Unlock iPhone 3g 4.21 with no service

[Shockz]

I upgraded to the iPhone 4. I would like to unlock my iPhone 3g. I have jailbroken it, and am trying to unlock it using this guide (Apple, iPhone and iPad Forums at ModMyi - How to Unlock the iPhone [ultrasn0w]) but I have no servce, and can not use Cydia even when I connect to my wifi. How can I unlock my iPhone 3g with no service? I use AT&T. I've searched the forum but have not fond anything.

Thanks

[iYeow]

Go to settings > general > about > modem firmware. If you dont have 05.13.xx or lower , then run redsnow rc8 and install iPad baseband update

[Shockz]

I have modem firmware 5.15.04. What would I do in this case?

[Mes]

Do what iYeow advised above.

[iYeow]

Run Redsn0w RC8 , browse to stock 4.2.1, choose only option : ipad bb update, finish up the process. You know unlocking with ipad bb will break your gps function.

Here is Redsn0wRC8