No Service on iPhone 3 when entering a new sim card?

I'm trying to set up this iPhone for my uncle. My mom gave it to him for Christmas, it was hers. It's in perfect condition and everything. I restored it, reset network settings 3 times. But I'm still getting the "No Service" thing. Is there any way to fix this without contacting his service provider?
AT&T, by the way.

Added (1). Not a faulty sim card, either.

It might be a faulty sim card, i had the same problem and mine was faulty or you might neet to register it.

Register it