I bought a softbank mobile phone in Japan and installed a domestic memory card. I can play songs but cannot set it as a ringtone. What should I do?

If you continue to use a Japanese operator, it can be used globally, but it is expensive.

If you want to take a China Mobile or China Unicom card back home, you may need to go to a mobile phone store to modify it, because Japanese mobile phones have different standards from China, and Chinese mobile phone cards cannot be used. The most obvious thing you should know is that Japanese mobile phones cannot send text messages to Chinese mobile phones. They use mail, not SMS. If you only care about appearance, then modify it, but the internal quality will definitely be greatly reduced after modification.