MNP (Mobile Number Portability) is a system that allows you to switch carriers while keeping your mobile phone number. Introduced in Japan in October 2006, it has significantly promoted competition among carriers. Before its introduction, the hassle of changing numbers was the biggest barrier to switching, but MNP enabled users to freely compare rates and services while retaining their number.
Number portability and MNP refer to the same concept, but MNP specifically applies to mobile phones. Fixed-line number portability is called LNP (Local Number Portability) and is used when migrating to Hikari Denwa. Since MNP's introduction, approximately 5-7 million MNP transfers occur annually in Japan, serving as the institutional foundation for the rapid growth of MVNOs (budget SIMs).
MNP procedures have been greatly simplified in recent years. Previously, you had to call your current carrier to obtain an MNP reservation number (valid for 15 days) and then sign a new contract at the destination carrier's store. Since 2023, MNP fees have been essentially eliminated, and same-day online processing (MNP one-stop method) is now available. With the one-stop method, you only need to complete the process on the destination carrier's website, eliminating the need to contact your current carrier. With eSIM-compatible devices, the entire process from application to activation can be completed in as little as tens of minutes.
Note that even with MNP number transfer, carrier email addresses (@docomo.ne.jp, @ezweb.ne.jp, @softbank.ne.jp) generally cannot be transferred. Since 2021, each carrier has offered a "mail portability service" (330 yen/month), but long-term migration to Gmail or similar services is recommended. Also, depending on the SIM card switchover timing, there may be a brief period when calls and data are unavailable. Review the latest procedures in the MNP procedure guide.