Ended up switching back to AT&T due to Int'l roaming issues in Asia with T-Mobile:
China Mobile's network is unusable. I was never able to get China Unicom to work (previous poster indicated success, but with some difficulty)
Paying for the 7-day package resulted in absolutely no benefit in Japan and China. No difference in speed in Japan and still completely unusable in China.
Basically unusable in Guam. Not fast enough for Google Maps.