Makes a big difference.
Use the SEARCH feature and look for "JAPAN". Been a lot of threads about it. In any case you will need to have the device unlocked before using any local SIM. Here is a link to get you started: New Bold 9000 Going To Japan and Need Advice on Roaming ATT Cingular
Previously there was very limited US BB connectivity in Japan since they use different frequencies. With the newer devices (9000 included) and some add on capability by some Japanese providers, there has been better connectivity. I have not kept up with it as it is constantly changing and I no longer travel there and therefore have no need.