When I went over none of our phones worked. We were all with telstra, and telstra said yeah it'll work......it didn't.
Anyway the deal is, you've got to hire a phone when you get there.
Docomo, au by KDDI and SoftBank are the main mobile service providers. And don't try and buy one of their phones, it won't work back in australia.
more info here:http://www.japan-guide.com/e/e2223.html