Switch Mobile Carriers in Japan Without Losing Your Number

2026年9月8日

Switch Mobile Carriers in Japan Without Losing Your Number

Use Mobile Number Portability, or MNP (keitai denwa bangō portability), and do not cancel your current line yourself. Apply to the new carrier as an MNP transfer, complete identity checks, receive or download the new SIM, and activate it. Your old mobile contract normally ends when the number moves to the new carrier.

For many online applications, Japan’s MNP One-Stop system means you no longer need to request a reservation number from your old carrier. The traditional reservation-number method is still available when One-Stop is unsupported or when you apply at a shop.

This guide is for foreign residents, workers, and students who already have a Japanese mobile number and want to change carriers while keeping it.

The essentials

Select “MNP” or “transfer an existing number,” not “new number,” when applying.
Use One-Stop online if both carriers support it; otherwise obtain an MNP reservation number (MNP yoyaku bangō).
Make sure the subscriber’s name and personal details match at both carriers.
Do not cancel the old line before the transfer is complete.
Check your phone’s compatibility, SIM-lock status, remaining device payments, carrier email, and bundled services before activation.

TOC

What MNP keeps—and what it does not

MNP keeps the eligible Japanese mobile telephone number, not the entire contract. The new carrier opens a new service contract, while the old carrier’s contract ends after the transfer is activated.

You can normally keep:

Your Japanese mobile number
The contacts stored on your phone or cloud account
Messaging accounts that are independently registered and properly backed up
Your existing handset, if it is unlocked and technically compatible

MNP does not automatically transfer:

Your old rate plan or discounts
Carrier-specific voicemail and optional services
A carrier email address such as an address ending in @docomo.ne.jp, @ezweb.ne.jp, or @softbank.ne.jp
Points, family discounts, content subscriptions, or payment services tied to the old account
SIM settings, eSIM profiles, or network configuration

Some operators offer a paid service that lets former customers retain a carrier email address. This is separate from MNP and usually requires action within the operator’s deadline.

ここがポイント: Moving the phone number and preserving everything connected to the old carrier are different tasks. Make a list of the services that use your old carrier account before you activate the transfer.

Choose between One-Stop and the reservation-number method

The best method depends mainly on where you apply and whether both services participate.

MNP One-Stop: usually easiest online

With MNP One-Stop (MNP wan-sutoppu), you begin at the new carrier’s website. During the application, you are redirected to the old carrier to sign in and authorize the transfer. You then return to the new carrier’s application.

The system began on May 24, 2023. Its practical advantage is simple: you do not have to obtain and type an MNP reservation number separately.

One-Stop generally requires:

An online application
A participating old carrier and new carrier
Access to the login credentials for your old-carrier account
An account that can complete the procedure without special manual handling

Participation has expanded beyond Japan’s four major mobile networks to various lower-cost services. The list can change, so confirm it on the destination carrier’s current MNP page before applying. Rakuten Mobile, for example, publishes a current list of services supported by its One-Stop process.

One-Stop may not be available when:

You apply at a physical shop
Either service is not a participant
You have already obtained a reservation number
The old account cannot be authenticated online
A corporate, family, user-registration, or account-name issue needs staff assistance

Two-Stop: use an MNP reservation number

The traditional process is sometimes called the Two-Stop Method. First, request an MNP reservation number from the old carrier. Then provide that number when applying to the new carrier.

The reservation number itself is not your telephone number. It is a temporary authorization code used to move the line.

A reservation number commonly remains valid for 15 days including the issue date. The new carrier may require more than a few days to remain when it receives your application. For example, au’s online shop requires at least 10 days of validity at application time.

If the reservation expires before the transfer is completed, the old line normally remains active. You must obtain another reservation number and try again.

Prepare these items before applying

Good preparation prevents most failed or delayed transfers.

1. Matching subscriber information

The name registered with the old carrier generally must match the name used for the new contract. Check:

Full name and its order
Roman letters, katakana, spaces, and middle names
Date of birth
Current residential address
Whether you are the contract holder or only the phone’s user

This is especially important for foreign residents. A carrier account created years ago may use an older address, a shortened name, or a different spelling from the current residence card.

If the accounts will not match, ask the old carrier whether a name change (meigi henkō) or transfer of contract ownership (meigi jōto) is necessary before requesting MNP. Do not assume the new carrier can correct the old account during the switch.

2. Identity and payment documents

Requirements vary by carrier and application channel, but foreign residents may be asked for:

A valid residence card (zairyū card) or special permanent resident certificate
A passport in some cases
A credit card or Japanese bank-account information
An additional document when the ID address does not match the application
A parent or guardian’s consent for a minor

The remaining period of residence can also affect an application for handset installment payments. A rejected installment application does not necessarily mean that the mobile service itself is unavailable; ask whether paying for the phone in full or bringing your own device is possible.

3. Access to the old account

Before starting One-Stop, confirm that you can sign in to services such as My docomo, My au, My SoftBank, or the relevant low-cost carrier portal. Reset a forgotten password first.

Also check whether the old carrier requires:

Two-factor authentication
A passkey or device authentication
A security PIN
Access through the current mobile line rather than Wi-Fi

4. A compatible, unlocked phone

Keeping a number does not guarantee that the same phone will work well on the new network. Use the new carrier’s compatibility checker for the exact model—not only the brand name.

Confirm:

Supported 4G and 5G frequency bands
Voice and emergency-call support
VoLTE compatibility
Physical SIM or eSIM support
Tethering and carrier-specific features
Whether manual APN settings are required

Phones sold in Japan from October 2021 onward are generally less likely to need a SIM-unlock procedure, but older devices may still be locked. Imported phones require extra care because they may lack important Japanese network bands or local technical certification.

The safest step-by-step switching process

Keep the old line working until the new SIM or eSIM is ready to activate. This reduces avoidable downtime and protects access to authentication messages.

Step 1: Compare the full cost, not only the monthly price

Before applying, check the new plan’s regular price after any introductory discount ends. Include:

Data allowance and speed restrictions
Voice-call charges or call-option fees
Contract administration fees
SIM or eSIM issuance charges
Handset cost
International calling and roaming
Shop-support fees, if applicable

Coverage matters too. A cheaper plan is not useful if reception is weak at your home, workplace, school, or usual train route.

Step 2: Audit the old account

Download recent bills and note anything that may continue or disappear:

Remaining handset installments
Family, home-internet, electricity, or credit-card discounts
Carrier email
Reward points
Paid content and device-protection services
A phone used for banking or account-recovery codes

Update critical accounts to a non-carrier email address before switching. Back up contacts, photos, messages, and authentication recovery codes.

Step 3: Start an MNP application with the new carrier

Choose wording such as:

MNP
Norikae (switching carriers)
Denwa bangō sono mama (keep the same telephone number)

Do not choose shinki keiyaku (new contract) if you want to retain the number.

For One-Stop, follow the link to the old carrier, authorize the move, and return to complete the new application. If One-Stop is unavailable, obtain a reservation number first and enter it exactly as issued.

Step 4: Pass identity verification

Enter information exactly as it appears on the accepted identity document. A small mismatch can stop automated verification.

If online verification repeatedly fails, do not submit altered spellings at random. Contact the new carrier and ask which format it accepts for foreign names. A shop application may be easier when your name is long, your documents use different scripts, or the contract holder and user are different.

Step 5: Wait for the SIM or prepare the eSIM

Do not activate a physical SIM before it arrives. If you selected eSIM, make sure you have:

A compatible device
Wi-Fi or another internet connection
Access to the activation app or QR code
A second screen if the QR code cannot be displayed and scanned on the same device

Do not delete an eSIM profile unless the carrier specifically instructs you to do so. Some profiles cannot simply be downloaded again without support.

Step 6: Activate the transfer

Start the MNP activation or line-switching procedure only when you are ready for the old line to stop working. Activation windows vary by operator, and a request made late in the day may be completed the following morning.

Once the number moves successfully:

The old SIM stops connecting.
The old mobile contract is terminated under the operator’s MNP process.
The new SIM or eSIM becomes responsible for the same telephone number.
The new plan’s billing begins according to its terms.

Install the new SIM or activate the eSIM, restart the phone, and follow the carrier’s setup instructions.

Step 7: Test the new line

Do not assume that seeing signal bars means everything works. Test:

An outgoing and incoming call
Mobile data with Wi-Fi turned off
SMS in both directions
Voicemail, if ordered
Tethering, if needed
Emergency-call capability as described by the carrier

If calls work but data does not, check the APN instructions. If nothing works, reconnect to Wi-Fi and contact the new carrier before repeatedly deleting profiles or resetting the phone.

What does MNP cost?

The transfer-out fee is generally zero at Japan’s major carriers, but switching may still create other charges. NTT Docomo and au both state that their MNP transfer handling fee is free, and SoftBank likewise states that it does not charge an MNP transfer-out fee.

Possible costs include:

A new-carrier contract administration fee
SIM issuance, eSIM, or shop-processing fees
The new handset price
Remaining installments on the old handset
Loss of family or bundled-service discounts
A paid carrier-email retention service
Charges under an operator-specific early-cancellation rule
A final bill containing usage or optional-service charges

Remaining device installments do not normally disappear when the mobile line ends. SoftBank, for example, states that installments continue to be collected unless the customer requests and qualifies for a lump-sum settlement.

As of August 22, 2026, customers should also check recently revised cancellation conditions rather than relying on old advice that cancellation is always free. SoftBank states that qualifying contracts started through a new subscription or MNP on or after July 1, 2026 may incur a cancellation charge of up to ¥1,100 if cancellation is requested within 12 months of service commencement. Conditions depend on the plan and contract, so check the explanation provided for your own line.

Common mistakes that can cost time or money

The most serious mistake is canceling the old line first. Once a number has been fully canceled, MNP may no longer be available, and recovery is not guaranteed.

Avoid these other problems:

Applying for a new number: Verify that the confirmation screen says MNP or number transfer.
Using a different account holder: Align the contract name before starting.
Requesting the reservation number too early: The validity period may run out while you compare plans or wait for documents.
Activating before the physical SIM arrives: The old line may stop while the replacement is unavailable.
Ignoring carrier email: Move important logins or arrange an email-retention service before its deadline.
Assuming the phone is compatible: Check the exact model and supported features.
Forgetting bundled discounts: Mobile cancellation can change the price of home internet or family lines.
Discarding the old account login: You may still need it for bills, points, installments, or tax records.
Starting activation just before a critical call: Allow time for verification, setup, and possible support.

Special situations and exceptions

MNP procedures are national in concept, but practical conditions are set by each operator. Differences are more likely to come from the carrier, application method, contract type, and customer status than from the municipality where you live.

Data-only plans

MNP is designed around eligible telephone numbers. A data-only SIM without an eligible voice number cannot normally be moved through standard mobile-number portability. Confirm the exact service type with both operators.

Corporate and employer-provided phones

A company-owned number belongs to the corporate contract, not automatically to the employee using the phone. Moving it may require the employer’s approval and a transfer of ownership before MNP.

Family accounts and registered users

The person using the phone may be different from the subscriber. Online systems can reject a transfer when user registration, family billing, or parental arrangements do not match the new application. Contact the old carrier before changing account relationships.

Outstanding bills

Unpaid charges can delay or prevent the procedure. Pay overdue amounts and confirm that the payment has been reflected before trying again.

Moving from Japan to another country

Japanese MNP transfers a number between participating services in Japan. It does not normally move a Japanese mobile number to a foreign carrier. If you need the number after leaving Japan, ask the current provider about continued service, roaming, low-cost plans, and identity or address requirements before departure.

Changing between brands in the same corporate group

A move such as au to UQ mobile or SoftBank to Y!mobile may be described as a number migration rather than ordinary MNP. The screens, fees, and treatment of discounts can differ even though the number stays the same. Follow the destination brand’s instructions.

If the transfer gets stuck

First identify which stage failed. That tells you which carrier should help.

Contact the old carrier when:

You cannot log in or authorize One-Stop
The subscriber name or account status is wrong
You need a reservation number
An unpaid balance or ownership issue is blocking release

Contact the new carrier when:

Identity verification fails
The application is rejected after authorization
The SIM has not arrived
The activation button is missing
Calls, SMS, or data fail after activation

Useful Japanese phrases include:

MNP de norikaetai desu — I want to switch carriers using MNP.
Denwa bangō o sono mama tsukaitai desu — I want to keep the same telephone number.
Keiyaku-sha meigi o kakunin shitai desu — I want to confirm the subscriber name.
MNP yoyaku bangō ga hitsuyō desu ka? — Do I need an MNP reservation number?
Kaitsū tetsuzuki ga kanryō shimasen — The activation procedure will not complete.

Take screenshots of error codes and confirmation pages. Do not post reservation numbers, residence cards, passwords, or QR codes publicly.

Current checklist before you press “activate”

MNP One-Stop has made online switching much easier, but the final activation still changes two contracts at once. Pause and check:

The new plan and exact device are compatible.
The contract holder’s details match.
The new SIM is in hand, or the eSIM setup is ready.
Important data and authentication methods are backed up.
Carrier email and bundled services have been handled.
Remaining device payments and possible cancellation charges are understood.
You have Wi-Fi and enough time to troubleshoot.

The practical watchpoint is the activation moment: once the number moves, the old line stops. Choose a time when you can test calls, SMS, and mobile data immediately—and when both carriers’ support channels are available if something goes wrong.

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