How to use a mobile phone when traveling to Japan?

You can use your mobile phone as usual, but you need it to support WCDMA(3G network standard) or Unicom's 4G network, and then you should open the international roaming service in advance.

Roaming service means that mobile phone users can continue to use their mobile phones in other areas outside their business areas. Roaming is divided into domestic roaming and international roaming, as well as roaming in Taiwan, Hong Kong and Macao. Roaming is a term commonly used by mobile phone users, which means that users of cellular mobile phones can continue to use their mobile phones in other regions or countries when they leave their own regions or countries. Roaming can only be carried out between connected domestic cities with compatible network standards, or between regions or countries that have signed bilateral roaming agreements.

International roaming services can be divided into "automatic roaming" and "non-automatic roaming" The so-called "automatic roaming" means that the communication system used in other countries or regions is the same as that in your own country, so you can use the original machine and number locally, such as in European countries; "Non-automatic roaming" is because the communication system in the country or region is different from that in China, so it may be used by "changing the number" or "changing the machine", such as Japan and South Korea.