Originally Posted by MSPeconomist

Your cell phone carrier(s) should be able to tell you or you might need to check what bands Japan uses versus what bands are available on your particular phone models.

Note that some countries don't (officially) permit device usage in the immigration and customs area, but this might not be enforced, especially if one is discreet. Quick email or text messages might be easier than voice calls. I don't know what Japan's policy is.