There is GSM 3G service in Japan. Also the old GSM/CDMA divide isn't really a consideration these days, since with the advent of 3G things started to converge. Just about nobody uses the "CDMA" 3G standard, CDMA2000, these days. In fact, 3G and LTE are all based on CDMA air interface.

Let 's keep discussing this in the Japan prepaid SIM thread:
http://www.flyertalk.com/forum/trave...sim-japan.html