How to get my iPhone 4S to read my sims card?

I bought an iPhone from a friend of mine, it's for AT&T. I went to get it factory unlocked for my tmobile sims card but it won't read it. The place I took it to showed me on the computer that it was unlocked and the message " congratulations your iPhone has been unlocked" displayed wen connected to iTunes. They refunded the money i paid because it wouldn't read my sims or any of their sims. The guy told me that it could be possible that I had a Japanese iPhone and I would have to get it unlocked another way. They told me that Japanese iPhones block the factory unlock. I was looking for anyone who knows anything about wat I can do to unlock my iPhone.

It would be better if you contact with the phone company or the shop from you bought it. They can help you on this. Because as they sell this sets so there may be more customers who have the same types of problems.