If I recall correctly, there aren't any GSM providers in Japan - meaning it's never going to make it to Japan until Apple makes TDMA version of the phone.
Rogers is in the process of de-commissioning all of its TDMA.Isn't TDMA what preceded GSM? I'm pretty sure there's at least one or two GSM providers in Japan.
At any rate, don't expect the iPhone there until Apple can promise FOMA or similar 3G+ Internet speeds.