All phone numbers should always be entered using the + notation. If a number is from NANP (e.g. Canada, US) it begins +1 since 1 is the country code for NANP. Japan's country code is 81 so Japanese number should begin +81. Generally, if you are given a foreign number begins with zero(s), you drop the leading zeros and prepend the country code. One exception to this rule is Italy, where phone numbers can actually begin with a "0" and rewriting can require a bit more information.
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