What Is MNP (Number Portability)?
MNP (Mobile Number Portability) is a system that lets you keep your mobile phone number when you change carriers. Introduced in Japan in 2006, it created an environment where users can freely choose their carrier. Understanding how number portability works helps you avoid trouble and complete the switch smoothly.
Before MNP, changing carriers meant getting a new number, so you had to notify every contact and update your registrations everywhere. With MNP you can compare plans and service quality and pick the carrier that suits you while keeping the number you already use.
How MNP Works Technically
Number Management Structure
MNP relies on carriers sharing a record of which carrier each phone number currently belongs to. When a port completes, that record is rewritten so the same number works on the new carrier's line. The number a caller dials does not change, so incoming calls reach the new carrier's network.
The Role of the MNP Reservation Number
Switching by the conventional route (the two-stop process) requires an "MNP reservation number": a 10-digit code you obtain from your current carrier and present to the carrier you are moving to. The reservation number is valid for 15 days including the day it is issued, and if it expires you simply request a new one.
MNP Switching Steps (Conventional Process)
- Step 1: Obtain an MNP reservation number: Apply to your current carrier by phone, on the web, or in a store. Which channels are available differs by carrier, so check the carrier's own instructions
- Step 2: Sign up with the new carrier: Present the reservation number when you sign the new contract. You will need identification and a registered payment method
- Step 3: Switch the line: Insert the new SIM card and complete the activation procedure. For online switches, run the activation from the dedicated page
- Step 4: The old contract ends automatically: Your old contract is canceled the moment the line switch completes. There is no separate cancellation to file
MNP One-Stop Process
The "MNP one-stop process" began on May 24, 2023. When both the carrier you are leaving and the carrier you are joining support it, a web application at the new carrier alone completes the switch, and no MNP reservation number is needed. The two routes exist side by side: for combinations that are not supported, and for applications made by phone or in a store, you still use an MNP reservation number as before.
With the one-stop process, you start the application on the new carrier's website and are then taken to your current carrier's authentication screen, where you confirm your identity and consent to the switch. Check whether your particular combination is supported in the instructions published by both carriers before you begin.
Things to Watch Out for When Switching
- Carrier email: Carrier addresses such as @docomo.ne.jp can be kept after switching if you subscribe to the paid carry-over service. The application window differs by carrier, so check the conditions as soon as you decide to switch
- SIM lock: SIM locks are banned in principle, but depending on when and where a handset was sold, some devices still need to be unlocked. Confirm that your handset will work on the new carrier before you apply
- Costs of ending the contract: Depending on your contract, charges may remain when you cancel, and if you bought your handset in installments the remaining balance is still due. Ask your current carrier what the final bill will be
- Service interruption: While the line is being switched there is a stretch of time when calls and data do not work. How long that takes depends on the procedure and the carrier, so avoid days when you are expecting important calls
- Transferring other services: Carrier billing, point programs, and family discounts may be lost when you switch. Check them in advance
MNP Fees
Porting-out fees are free when the switch is handled on the web. Fees may apply when the procedure is done by phone or in a store (per Ministry of Internal Affairs and Communications guidance, as of August 2026). The contract processing fee charged by the new carrier varies by carrier and by plan, and some carriers do not charge it on online-only plans. Check whether a fee applies, and how much, on each carrier's fee schedule before you apply.
Smart Switching Strategies with MNP
Take Advantage of Switching Campaigns
Carriers sometimes run promotions for people who join by MNP, such as cashback or discounts on handsets. Both the terms and the period differ from carrier to carrier, so line up several carriers' offers at the moment you are ready to apply. Promotions can come with conditions attached, so do not judge by the discount alone.
Key Points for Comparing Plans
- Monthly base fee: Compare the total including the data allowance and calling options. A low headline fee can end up expensive once the options you need are added
- Data allowance: Check how much data you actually used over the past three months and pick a matching plan. Buying far more headroom than you use is wasted spending
- Calling options: Judge whether you need an unlimited or time-capped calling option based on how often and how long you call. Compare the option fee against the call charges you would otherwise pay
- Family discounts: Check the discount for having the whole family on the same carrier. Switching together can produce meaningful savings
- Device installments: If you buy a handset from the new carrier, check the installment terms and the total cost. Pay attention to the return conditions on residual-value plans
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 widening user choice. Before MNP, the hassle of changing numbers was a major barrier to switching, and the resulting "lock-in effect" that tied users to incumbent carriers was seen as a problem. Mobile phone numbers themselves took their present form after the 1999 transition to 11 digits.
After MNP arrived, the range of plans to choose from widened and comparing carriers before signing up became routine. Through the 2020s, policy work by the Ministry of Internal Affairs and Communications has revisited the costs and the handset restrictions around switching, and SIM locks are banned in principle. Porting out on the web being free of charge is part of that same review (as of August 2026).
MNP to MVNOs (Budget SIMs)
Porting from a major carrier to an MVNO (budget SIM) is one way to revisit what you pay for mobile service. Fees vary widely by operator and data allowance, so compare what you pay now against the price of the allowance you actually need at the new operator. Questions about number ranges and the switching procedure are also collected in our mobile phone FAQ.
Things to Watch When Switching to an MVNO
- Data speeds: MVNOs lease their lines from major carriers, so speeds tend to drop during busy hours such as lunchtime and early evening
- In-store support: Many MVNOs have no physical stores, so face-to-face support may not be available. Take that into account if you are not used to handling things online
- Loss of carrier services: Carrier-specific services such as carrier billing, carrier email (available for a fee) and family discounts stop being available
- Device compatibility: Check the new MVNO's supported device list to confirm that the handset you are using will work
There are two routes, the reservation number has an expiry date, and the costs and handset conditions differ by carrier. Keep those three points in mind and the MNP procedure rarely goes wrong. MNP works for numbers in the 090, 080 and 070 ranges alike.