I need some, help. I don't know why i'm getting a message that reads:

Fixed Number Dialing Active
Insert an unlocked and valid SIM to activate iPhone

With this message showing, after I call to the *#307# I try to call to the 0, and nothing happend. The iPhone sais Called Faild.

It shows this message with the original AT&T SIM.
I don't have access to AT&T to get a new SIM.

I have restored the iPhone serveral times, but nothing happends. The message is still there.