What Is MNP (Number Portability)?
MNP (Mobile Number Portability) is a system that lets you keep your current mobile phone number when switching carriers. Introduced in Japan in 2006, it created an environment where users can freely choose their carrier. Understanding MNP helps you avoid trouble and complete the switch smoothly.
Before MNP, changing carriers meant getting a new number, requiring you to notify all contacts and update registrations everywhere. MNP eliminated this barrier, letting you compare plans and service quality while keeping your number. MNP-compatible SIM cards are a good reference for the switching process.
How MNP Works Technically
Number Management Structure
MNP operates through a central database that manages the association between phone numbers and carriers. When a number is ported, this database is updated so the same number works on the new carrier's network. Incoming calls are routed to the correct carrier by referencing this database.
The Role of the MNP Reservation Number
The switching process requires an "MNP reservation number" - a 10-digit code obtained from your current carrier and presented to the new one. The reservation number is valid for 15 days from the date of issue. If it expires, you can request a new one at no charge.
MNP Switching Steps
- Step 1: Obtain an MNP reservation number: Request from your current carrier by phone, web, or in-store. Online is the most convenient
- Step 2: Sign up with the new carrier: Present the reservation number when signing a new contract. ID and a credit card are required
- Step 3: Switch the line: Insert the new SIM card and complete the activation procedure. For online switches, use the dedicated activation page
- Step 4: Automatic cancellation of old contract: Your old contract is automatically canceled when the line switch completes. No separate cancellation is needed
MNP One-Stop Process
Since May 2023, the "MNP one-stop process" allows you to complete the entire switch through the new carrier alone. You no longer need to contact your current carrier for a reservation number. Major carriers (Docomo, au, SoftBank, Rakuten Mobile) and major MVNOs support this process.
With the one-stop process, starting the switch on the new carrier's website redirects you to your current carrier's authentication page for identity verification and transfer consent. Everything is completed online with no need to visit a store. Having a SIM-free smartphone ready beforehand ensures a smooth transition.
Things to Watch Out for When Switching
- Carrier email: Carrier emails (@docomo.ne.jp, etc.) can be kept via a paid option (around 330 yen/month). You must apply before switching
- SIM lock: Devices sold after October 2021 are SIM-lock free by default. Older devices may need SIM unlock first
- Early termination fees: Abolished since July 2022, but remaining device installment payments must still be paid
- Service interruption: Online switches may cause a few minutes to a few hours of downtime. Avoid days when important calls are expected
- Service transfers: Carrier billing, point programs, and family discounts may be lost when switching. Check in advance
MNP Fees
Since April 2021, MNP transfer fees have been eliminated. Previously, a 3,300 yen transfer fee was required, but it was abolished following MIC guidance. However, a contract processing fee (around 3,300 yen) may apply at the new carrier. Online-only plans often waive this fee as well, so use online procedures to minimize costs.
Smart Switching Strategies with MNP
Take Advantage of Switching Campaigns
Many carriers offer cashback, device discounts, and other promotions for MNP new subscribers. Campaign details vary by season, so compare multiple carriers. Year-end (March) and New Year periods tend to have the biggest promotions.
Key Points for Comparing Plans
- Monthly base fee: Compare the total including data and calling options. A low base fee may become expensive once necessary options are added
- Data allowance: Check your actual data usage over the past 3 months and choose an appropriate plan
- Calling options: Decide whether an unlimited calling plan (1,000-2,000 yen/month) is needed based on your call frequency. If LINE calls suffice, it may be unnecessary
- Family discounts: Check family discount amounts when the whole family uses the same carrier. Switching together can yield significant savings
- Device installments: If purchasing a device from the new carrier, check installment terms and total cost. Pay attention to residual value plan return conditions
History and Policy Background of MNP
Japan's MNP system was introduced on October 24, 2006, with the policy goals of promoting competition among carriers and expanding user choice. Before MNP, the hassle of changing numbers created a "lock-in effect" that kept users tied to incumbent carriers. The introduction of MNP significantly stimulated competition, leading to more diverse plans, improved network quality, and better device lineups. Since 2020, MIC guidance has achieved free MNP transfers, abolished early termination fees, and banned SIM locks by default, further lowering switching barriers. Note that mobile phone numbers themselves were established in their current form after the 1999 transition to 11 digits.
MNP to MVNOs (Budget SIMs)
Switching from a major carrier to an MVNO (budget SIM) via MNP can dramatically reduce your phone bill. MVNO monthly fees typically range from 1,000 to 3,000 yen - often less than half of major carrier prices.
Things to Watch When Switching to an MVNO
- Data speeds: MVNOs lease lines from major carriers, so speeds may drop during peak hours (lunch, evening)
- In-store support: Many MVNOs lack physical stores, so in-person support may be unavailable
- Loss of carrier services: Carrier billing, carrier email (can be kept for a fee), and family discounts become unavailable
- Device compatibility: Verify that your current device works with the new MVNO by checking their supported device list
By understanding MNP and choosing the right carrier for your usage style, you can optimize costs while enjoying a comfortable communication environment. MNP is available for all number bands - 090, 080, and 070.