My friend is in Japan. His telephone number is 0663. Where does it come from?

The telephone number in Japan consists of three parts.

[Example: 03 (area code)+1234 (office number) +5678 (receiver number)]

06 is indeed the area code of Osaka, but there should be two numbers after 63. ...

In addition, short messages in Japan are generally sent by mail, not directly by mobile phone number, because it is a 3G network. I don't know how your friend sends you Chinese messages on Japanese mobile phones.