- What MNP does and does not carry over
- One-stop versus two-step
- When your old contract ends
- The rules on transfer fees
- What to check before switching
The short answer
MNP (mobile number portability) is the procedure for keeping your current phone number when you move to a different mobile carrier. In Japan there are now two ways to do it: the one-stop method, where you only apply to the new carrier, and the two-step method, where you first get an MNP reservation number from your current carrier and then apply.
The procedure itself is rarely where people trip up. The problems come from what they did not check beforehand: carrier email, family discounts, handset instalments, and whether their phone will work on the new network. The rules described here were checked against the Ministry of Internal Affairs and Communications (MIC) mobile phone portal; the check date is shown at the top and bottom of this article.
What MNP is
A phone number is assigned when you sign a contract with a carrier. In the past, changing carrier meant changing number, and telling every client and friend the new one. MNP removes that burden.
Your number is registered in more places than you might think: business cards, clients' contact lists, your bank and local government records, and services that send login codes by SMS. If the number stays the same, none of that needs updating. A simple way to decide whether MNP matters to you is to think about how many places your number is registered.
What MNP carries over is the number. Your old carrier's email address, discounts and points do not necessarily come with it. We return to this below.
One-stop and two-step methods
The one-stop method
This method started on 24 May 2023. You apply only to the new carrier and the transfer goes ahead; no MNP reservation number is needed. It removed the step of going to your current carrier's website to request a number.
It works only when both the old and the new carrier support it. Check each carrier's information to see whether they do.
The two-step method (using an MNP reservation number)
This is the original method.
- Ask your current carrier to issue an MNP reservation number.
- Apply to the new carrier using that number.
- Activate the new SIM card or eSIM when it arrives.
The MNP reservation number has an expiry date. How long it lasts, and how much time must remain on it when you apply, should be checked in the carriers' own information. If it expires, you request a new one.
| What to look at | One-stop | Two-step |
|---|---|---|
| MNP reservation number | Not needed | Issued by your current carrier |
| Where you apply | New carrier only | Current carrier and new carrier |
| When you can use it | Both carriers support it | The long-standing method |
Activation, cancellation and fees
Do not cancel your current contract first
A common worry is when to cancel the old contract.
With MNP, you do not cancel it yourself. If you cancel first, the number itself is gone and there is nothing left to transfer. MIC states that your current contract is not cancelled until the contract with the new carrier is complete. Once the switch goes through, the old contract ends.
When switching with MNP, do not cancel your current contract yourself beforehand. Cancelling releases the number, and it can no longer be transferred.
Choose when to activate
When the new SIM card or eSIM arrives, you complete activation online, by phone or similar. During the changeover there may be a short period with no calls or mobile data. Avoid times when you are expecting an important call or are out; do it at home or in the office where Wi-Fi is available.
Whether your old carrier charges the final month in full or pro rata when you switch mid-month differs by carrier. Check your current carrier's information.
Fees and retention
According to MIC, transferring your number out of your current carrier is free if done online. If done by phone or in a shop, a fee of up to 1,100 yen may apply. Any sign-up fees at the new carrier are separate and set by each carrier, so estimate the two separately.
MIC also states that your current carrier is prohibited from making sales efforts to stop you from porting your number without your consent.
What to check before switching
Before starting, work through these one at a time.
- Carrier email. An email address tied to your carrier's domain may stop working when you leave. Some carriers offer a way to keep it, so check your current carrier's information. If your bank, online shops or government services use that address, change them to another address before switching.
- Family and bundle discounts. If your family shares a carrier, or you get a discount bundled with home broadband, one person leaving may change the discount for everyone else.
- Handset instalments. Switching does not cancel what you still owe on your phone. How the remainder is paid depends on your contract. If you are on a programme where returning the handset reduces what you pay, check its conditions too.
- Whether your phone will work. SIM locks have in principle been banned on phones released in Japan from October 2021 onward, but older handsets from the major carriers may still be locked. Unlocking is free online; a fee may apply by phone or in a shop. Even unlocked, a phone may get a weak connection if it does not support the new network's frequency bands.
- Physical SIM or eSIM. Decide which one you will use with the new carrier, and check your phone supports it.
- Anything billed with your phone. Check services you pay for through your phone bill, and what happens to any points you have built up.
An example, step by step
Take a sole trader whose mobile number is printed on their business cards, moving from a major carrier to another provider.
- List the services registered to their carrier email and change them to another address.
- Check the family discount and the remaining handset payments on the current carrier's member page.
- Check whether the new provider supports the one-stop method. If not, request an MNP reservation number from the current carrier.
- Apply to the new provider and receive the SIM card or eSIM.
- Activate it on a quiet day for calls, somewhere with Wi-Fi.
- Confirm that outgoing and incoming calls, SMS and mobile data all work.
No new business cards, no messages to clients about a new number — that is the main benefit of MNP. Skip steps 1 and 2, though, and you find out later: emails that stop arriving, or a discount that shrank more than expected.
In short
MNP lets you keep your phone number when you change carrier. Since May 2023 in Japan, the one-stop method lets you switch without a reservation number when both carriers support it; the two-step method still uses an MNP reservation number. Do not cancel your old contract first, and transferring out online is free. Before you start, check carrier email, family discounts, handset instalments and whether your phone will work on the new network.