There are two (possibly even more as of this writing) GSM carriers in Japan. They are NTT DoCoMo, Inc and Vodafone K.K. (J-Phone.
He would technically not need another phone or SIM to be able to make and recieve calls...BUT it will cost him much more per minute (whatever Cingular charges for world rates).
I would suggest calling cingular and finding out about the feature. You might have to activate it (usually free) and they will tell you how much the minute rate will be. I traveled to Dominican Republic and Russia with my T-Mobile phone and had no problems.
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My son is going to be travelling to Japan in December. He has an unlocked GSM phone and we use Cingular/AT&T.
Does anyone know if he will be able to use the phone in Japan, possibly by getting a SIM card from a Japanese carrier?
I've been reading in these responses that Japan doesn't use GSM. I would sure like to know before he goes. If anyone has any reliable information about cell phones in Japan, please post it.
I would like to know the best way for him to call locally in-country while in Japan, as well as back home to the states.