How to Switch Mobile Carriers in Japan and Keep Your Number with MNP
MNP lets you switch mobile carriers in Japan while keeping your current phone number. Do not cancel your old line first; check one-stop eligibility, MNP reservation details, device compatibility, documents, and activation timing.
MNP lets you change mobile service providers while continuing to use your current phone number. If both carriers support MNP one-stop for the application channel you use, you can begin on the new carrier’s website without obtaining a reservation number first. If one-stop is unavailable, you must request an MNP reservation number from your old carrier and enter it when applying to the new carrier.
The most important rule is: do not cancel your old line before the MNP transfer is complete. Once the number has been canceled, you may lose the right to transfer it.
What is MNP, and what does it preserve?
MNP stands for Mobile Number Portability. It normally transfers an eligible phone number. The following items do not move automatically:
An email address issued by your old carrier.
Reward points and membership benefits.
Data stored in the carrier’s app or cloud service.
Unused data allowance.
Family options or bundled discounts.
Outstanding device installment payments.
Internet contracts or other bundled services.
Before switching, list every service connected to your old number and account. Some options may need to be canceled separately.
How are MNP one-stop and the traditional process different?
MNP one-stop
Japan introduced MNP one-stop on May 24, 2023, for participating carriers and online procedures. According to the Japanese government’s public information portal, eligible users can start the request on the new carrier’s website without first obtaining an MNP reservation number from the old carrier.
One-stop does not mean that every carrier, brand, and application channel participates. Check the current list and the new carrier’s instructions when you apply.
Using an MNP reservation number
If you cannot use one-stop:
Ask your old carrier to issue an MNP reservation number.
Record the number and its expiration date.
Apply to the new carrier while the number remains valid.
Complete identity verification and receive the SIM or eSIM.
Switch the line according to the carrier’s instructions.
Carriers set both the validity period and the minimum validity remaining when they accept an application. For example, NTT Docomo currently states that its MNP reservation number is valid for 15 days, including the issue date. A new carrier may still require more remaining days to process an order. Check the exact provider’s conditions instead of applying one deadline to every carrier.
What should you check before switching?
Subscriber name and account details
The subscriber’s name, date of birth, and other account information should match across the old carrier, identity document, and new application. The procedure may differ if the line is registered to a family member or company.
Is the number eligible for MNP?
Not every number or data service can be transferred. A data-only SIM usually does not have a voice number that can be ported through the ordinary MNP process. Ask the current provider if you are unsure.
Will the phone work on the new network?
Check:
The phone model and model number.
SIM-lock status, if relevant.
Supported frequency bands and the carrier’s compatibility list.
Whether you need a physical SIM or eSIM.
Any APN or other configuration required.
Keeping the number does not guarantee that the device will work properly on the new network.
Device balance and contract obligations
MNP ends or changes the old mobile service, but device installment payments may continue. Check the final bill, any cancellation charges, lost promotions, and how the remaining device balance will be paid.
Step-by-step MNP process
Step 1: Back up important information
Save contacts, photos, authentication data, and login details. If you use a carrier email address, change the registered email at banks, social networks, and important services before the address stops working.
Step 2: Review the old contract
Check:
The billing cutoff date.
Cancellation charges or conditions.
Device installments.
Whether a SIM or router must be returned.
Linked family plans and Internet services.
Do not assume that switching at the end of the month is always cheaper. Final-month billing rules differ by provider.
Step 3: Choose the new carrier
Compare coverage, data allowance, calls, SMS, tethering, eSIM support, language support, and total cost. Check coverage at home, work, and along your commute rather than relying only on a nationwide map.
Step 4: Use one-stop or obtain an MNP reservation number
If the new carrier offers one-stop, follow its authentication flow. Otherwise, request a reservation number from the old carrier through its website, app, phone service, or store, depending on the available methods.
Step 5: Apply to the new carrier
You may need:
An accepted identity document.
An address in Japan.
A payment method.
The phone number you want to transfer.
The MNP reservation number for the traditional process.
An IMEI or EID for eSIM or device checks.
Enter your name and address exactly as shown on your documents.
Step 6: Receive the SIM or eSIM information
For a physical SIM, wait for delivery or collect it from the specified location. For an eSIM, you need a compatible device and usually a Wi-Fi connection to download the profile.
Step 7: Switch the line
Submit the activation request or use the automated phone channel described in the instructions. There may be a short period when the old line has stopped but the new network is not yet ready. Choose a time when you are not waiting for an important call.
Step 8: Test the service after activation
Test:
Outgoing and incoming calls.
Sending and receiving SMS.
Mobile data with Wi-Fi turned off.
Hotspot use, if needed.
Login to the carrier app.
Remove the old SIM or delete its configuration only after the transferred number works correctly.
How to prepare for switch day and avoid losing contact
Do not activate the MNP transfer immediately before a flight, job interview, important work shift, or expected delivery. Choose a period when you have stable Wi-Fi, enough battery, a charger, and time to resolve any identity-verification or setup problem.
Before switching the line, save the following information somewhere you can access without mobile data:
The new carrier’s order number and login details.
The MNP reservation number and expiration date, if applicable.
Support contact details for both carriers.
Screenshots or notes for the APN, eSIM QR code, and activation steps.
The identification and payment method used in the application.
Review important accounts that send one-time passwords to your phone number, including banks, credit cards, email, messaging apps, and work accounts. MNP keeps the number, so you normally do not need to update it in these services. However, SMS may be temporarily unavailable during the transfer. Avoid signing out of everything or changing phones at the same time unless necessary.
For a physical SIM, insert the new card only when instructed and retain the old one until testing is complete. For an eSIM, download the profile over Wi-Fi and do not delete the old eSIM merely as a troubleshooting attempt. Apple also advises against deleting an eSIM as a troubleshooting step unless the carrier directs you to do so, because you may need the carrier to issue a replacement.
After the transfer, test calls, SMS, and mobile data separately. If data fails while calls work, review the APN and mobile-data line selection. If nothing works, record the error message, restart the phone once, and contact the new carrier. Avoid repeatedly deleting profiles, rescanning a QR code, or resetting the phone until you know whether the activation code can be reused.
Where should you check MNP costs?
The Japanese government states that the transfer-out fee for web procedures was reduced to zero yen under revised guidelines, while some other channels may charge a fee within the applicable limit. The total cost of switching, however, is not limited to the “MNP fee.” Check:
Registration or issuance fees charged by the new carrier.
SIM or eSIM fees, if any.
The final monthly bill.
Contract cancellation charges.
Outstanding device installments.
Options or bundled services that lose a discount.
Conditions can change, so an article should not present one total price as applicable to every carrier.
Common mistakes
Canceling the old SIM first
This is the most serious mistake. MNP must begin while the number is still active and eligible.
Letting the reservation number expire
Request a new number if the new carrier requires more processing time than the validity remaining.
Mismatched subscriber details
Incorrect names, dates of birth, or addresses can cause verification to fail. Update the old account first if necessary.
Porting the number but forgetting carrier email
A carrier-issued email address may stop working or require a separate portability service. Change important login email addresses before switching.
Assuming the phone installment balance disappears
Switching carriers does not automatically erase device installments. Review the payment schedule after MNP.
Deleting the eSIM too early
If the new profile fails, you may lose both ways to connect. Follow the provider’s activation order.
Frequently asked questions
Is MNP one-stop available for every carrier?
No. Confirm that the old carrier, new carrier, and specific online channel all participate.
Can I keep my number while changing from a physical SIM to an eSIM?
Potentially, if the new carrier and device support it. Number portability and SIM format are separate matters.
When is the old SIM canceled?
The old service normally ends when the transfer completes, but the exact process depends on the carrier. Do not cancel it yourself beforehand.
Will I lose LINE when using MNP?
MNP does not delete the app. Still, back up your data and check the login method, email, password, and account-transfer settings before changing a device or SIM.
Can I use MNP while paying off my phone?
In many cases, yes, but the installment obligation normally remains. Check the contract and payment status.
Conclusion
MNP lets you change carriers without telling everyone a new phone number. The safe sequence is to check the old contract, confirm device compatibility, use one-stop or obtain a reservation number, activate the new service, and then test calls, SMS, and data. Never cancel the old number before the transfer is complete.
Want a better plan while keeping your Japanese phone number? Use NST Connect’s Find Your Plan tool to identify a plan suited to your data needs, device, and length of stay. The carrier decides whether the MNP application and number transfer are accepted.
Related articles
Participating one-stop carriers, fees, and processing conditions can change. Check the current documentation from both carriers before starting the transfer.