Japanese phones are generally WCDMA so you won't be able to.
However, the providers are selling world-compatible phones that have GSM, Sharp and Toshiba have a whole line of them. The tricky part is unlocking them, when I was in Japan last November I was looking into it but none of the current phones being sold could be unlocked (some of the older ones could be). Or even if you could unlock it, it was only with a firmware flash that disabled some of the functions and disabled use of Japanese (the main reason I wanted it). So if you do decide to go this route, make sure you do your homework on which model to get.
A friend of mine told me about these guys
link