Phone number format refers to the rules for writing phone numbers as text. In Japan, the standard notation separates area code, local exchange code, and subscriber number with hyphens, as in 03-1234-5678. This segmentation visually represents the number's structure and improves readability and memorability.
Domestic formatting patterns vary by number type. Landline numbers shift the hyphen position based on area code length: 03-1234-5678 (2-digit area code), 045-123-4567 (3-digit), 0166-12-3456 (4-digit), all maintaining 10 total digits. Mobile numbers use the standard 3-4-4 split: 090-1234-5678. Toll-free numbers use a 4-3-3 split: 0120-123-456.
For international notation, the E.164 format is standard. To express a Japanese number internationally, remove the leading 0 and prepend country code +81 (e.g., 03-1234-5678 becomes +81-3-1234-5678). Variations using spaces instead of hyphens (+81 3 1234 5678) or parentheses around the area code (+81 (3) 1234-5678) are also used internationally. RFC 3966 defines the tel: URI scheme (tel:+81312345678), used for phone links on web pages.
When entering phone numbers on websites or apps, format variations - presence or absence of hyphens, full-width vs. half-width characters, presence or absence of the leading 0 - become an issue. Phone number validation requires flexible design that accepts various input formats. Google's libphonenumber library is the de facto standard tool for normalizing and validating phone number formats across 200+ countries. See Phone Number Structure Guide for the overall numbering system and Japan Country Code Guide for international notation details.