[everybest]

I don't know what sort of deals the providers in the US have but make sure on the pricing before you go. As long as you do have a 3G phone, you should be able to use in Japan, but roaming charges were about $2 a minute when I was there.

The rent-a-phone companies at the Narita airport was pretty pricey the last time I checked, but free to receive calls, so I have rented from there once before, but for the most part, had friends and family call me, not vice-versa. You can just rent a sim card rather than a phone if your phone is already unlocked.

Actually buying a phone is a lot of hassle, especially through retail since you have to have proof of residence. If you really want one though, what I did was buy a keitai through yahoo auctions japan (still need a shipping location in Japan or overprice on ebay) and once you leave Japan, you can unlock the phone to be used in the States or wherever with a hypersim. You are, for the most part, restricted to DoCoMo phones, however, and internet options and 1seg TV doesn't work outside japan, even with a dataplan.