Get iphone to work w/ ATT PDA data plan?

My son lives most of the year in Germany and has an unlocked original iphone purchased there (Apple wasn't allowed to sell locked phones in Germany :-). He has a UK SIM, Czech SIM, and Asian SIM for when he travels to those areas. No problems. When coming to the US he had been using the SIM from his old iPAQ which is on my family plan and had been working fine. Last time he was here data wouldn't work (voice & SMS worked fine). ATT said that he now had to have a specific iphone data plan instead of the generic PDA data plan but that they couldn't add it to the account unless he purchased an iphone.

Is ATT blocking iphones unless purchased from them? Is his only option for the US to get a SIM from another carrier? Or is ATT blowing something and he just needs to make config changes?

Any thoughts from anyone on this would be very helpful!

Thanks,

An iPhone using an AT&T SIM card is required to have the appropriate iPhone data plan. It does not matter how the iPhone was obtained.