Go to Japan and send a message to China. ...

1. The domestic mobile phone system does not support Japan, so it cannot be used after coming to Japan.

2. It takes about 15 yuan RMB one minute to make a direct call from Japan. I guess you won't call either. You can use skype. If your mobile phone supports it, that's best. There are wifi wireless networks in many places in Japan.

The voltage in Japan is 1 10v, 60hz. See if your phone charger supports it.