iPhone 3g "no service"

[chargit]

I have a customer that brought me a 3g not jailbroke iPhone and he gets not bars and no service. I have done the usual....restoring, replace the antenna, cleaned the sim contacts, put a piece of a business card on top of the sim to make it have a better connection and no luck! the phone is not in warranty and looks to be in mint condition. every function works but it will not make a call.

any suggestions?