Number portability is a general term for systems that allow switching carriers or services while keeping your phone number. MNP (Mobile Number Portability) for mobile phones is the most widely known, introduced in Japan in October 2006.
For mobile MNP, you obtain an MNP reservation number from your current carrier and transfer the number when signing a new contract with the destination carrier. Since May 2023, the online MNP one-stop method has been introduced, completing the process through the destination carrier's procedures alone. Transfer fees are being eliminated by both source and destination carriers.
Number portability also exists for landlines, though it is less flexible than for mobile phones. Numbers can be transferred when migrating from NTT subscriber lines to Hikari Denwa, or when changing providers within the same area code zone. However, when moving to a different area code, or for numbers originally obtained from non-NTT providers, transfer may not be possible.
The spread of number portability has significantly promoted competition among carriers. Eliminating the hassle of number changes has enabled easy switching based on rate and service comparisons, resulting in lower communication costs and improved service quality. Approximately 5-7 million MNP transfers occur annually in Japan, serving as the institutional foundation for MVNO (budget SIM) growth. Fixed-line number portability (LNP) is used when migrating from NTT to Hikari Denwa or switching to other fiber phone services. Review procedures in the number portability guide.