"010" is not a valid area code within the United States because no area codes are permitted to start with "0" under the North American Numbering Plan. However, "010" is an international exit code for phones located in Japan.
Making an international call requires dialing the exit code of the country where the phone is located, then dialing the country code of the receiver's country. "010" is Japan's exit code. A person in Japan who wishes to call the U.S. must dial "010," then the U.S. country code, "1," then the receiver's phone number. However, someone in the United States who wishes to reach Japan must dial the U.S. exit code, "011," then Japan's country code, "81," then the receiver's number.