I hate to say this, but I wouldn't expect UMA to work over most hotel wifi systems . This is because most hotel wifi services I've seen require you to log on with a username and password, and to my knowledge, you can only access either open or WEP (key)-accessible wifi via UMA on TMO, not username/password protected wifi.

However, assuming Starbucks is still offering TMO Hotspots by then, you should be in luck at nearly any Starbucks; TMO's UMA-enabled phones just seem to seamlessly work at Starbucks' (and airport Hotspot) locations.

(oh, and Japan's cellular networks aren't on GSM, I'm pretty sure, so you'll likely need an entirely different cell phone there).