Whichever carrier though, it could easily turn out to be an American, 'gaijin thing' if you will, and thus maybe AU isn't interested.
I think it's more of a "Non-Japanese = inferior" mentality than anything else. Think about it: how many foreign-made phones have you seen AU selling? I could be way off base here, but I don't recall EVER seeing a Motorola or Nokia sold by AU. This is in contrast to DoCoMo and Softbank, who have throughout the years offered various phones other than the stock Sharp/Panasonic/Toshiba/NEC cookie-cutter crap everyone shoves down our throats.
In any case, I believe the iPhone will do very well here for the simple reason that it blows away ANY Japanese phone in terms of usability and coolness. I mean, the people who see my hacked Touch are astounded when they see me flipping through pics, using coverflow, and typing emails at 40 words per minute. Which of course brings us to what has already been mentioned a few times: the iPhone and iPod Touch right now are TERRIBLE for Japanese input. My J-friends with Touches all complain about how difficult it is to input kana/kanji - the predictive entry method works fine (albeit slow) but the conversion choices are VERY small and therefore difficult to press. Apple needs to do something to address Japanese input methods on the iPhone, or else it will be a tremendous flop. (except for me and my fellow gaijin, who will line up to buy one on launch day) ... hehe