Tokyo Metro started to be able to use mobile phones in almost every its place from this afternoon. Passengers can email or browse internet in trains or stations of Tokyo Metro. Also about the other subway in Tokyo, Toei Chikatetsu will start until the end of March. But must not talk loud with a mobile phone in a train in Japan. And each railway company asks to passengers to not use mobile phones near courtesy seats. If you will use your mobile phone by international roaming service, be careful to fee. It may very expensive. You had better to confirm the fee to your mobile phone provider before use.