Question: Does T-Mobile Phones work in Japan.

Answer: Yes, T-mobile phones work in Japan.  If you have international roaming, the phone will work.  If you want a local SIM card, the phone must be unlock to insert local SIM card from Japanese carriers.  The biggest problem in getting a local SIM card is that it required a Japanese National ID card.  You can only get a Japanese National ID card if you have a visa longer than 3 months.