Have anybody successfully used their existing AT&T sim on a jailbreak 3G iphone? I have winpwned my 3G iphone with custom ipsw. Activation was selected when I build the custom ipsw. I did not get any signal when I put my existing AT&T sim in. I have also tried on a custom ipsw without activation but the result was the same. I would really appreciate it if someone can offer some suggestion.

You cannot use that Activate option when creating your custom ipsw, go back and remove it and redo it. I did that and iTunes just activated the phone and it works, signal and all. And no I dont have an iPhone plan, never bought one or been on one.

Dixit