So, I guess that settles it. You can take the damn thing to the US and use it with At&T if you like but you can only use it with Softbank in Japan.
According to a post at mobile in Japan, one of their readers emailed Steve Jobs and got a reply saying:
Actually, the version of iPad sold in Japan does accept international SIMs.Well that is interesting. So which is it? Apple posts an FAQ (see Edit3 here) that is a direct translation from the US site, then updates the FAQ the next day (edit5, same post) to say it cannot be used with a micro-SIM other than Softbank's.
One thing is for sure, Apple sure screwed up this one. Either Steve Jobs is mistaken or we are looking at the third FAQ update by Apple Japan in as many days. If this was the US, it would be pretty easy to get your money back on a pre-ordered iPad due to the incorrect information being given out by Apple.
But I am 99.9% positive this will not happen for anyone in Japan who paid money thinking they were getting an unlocked device. Not only are you dealing with Apple, but softbank on top of that.