Can I only use the mobile phone card of Telecom to go to Japan?

Not necessarily. Japan also has WCDMA and GSM standard networks. In addition, if you are a mobile phone, GSM is enough. Although it is a bit expensive, the quality of the call is not a problem. If you go abroad, you can't make a phone call or make a global call. But the phone bill will be higher. If you go to Japan for a long time, you might as well buy a mobile phone number there. Mobile phone sales in Japan are rather strange. Basically, mobile phone cards and mobile phones are tied together for package consumption. But it's good to have an extra mobile phone. Just bring it back when you return home, because most Japanese mobile phones are not available in China. You can also use a mobile card when cracking.