2026 Guide
How to Keep Your Phone Number When Switching Carriers (MNP)
Sponsored / Contains affiliate links
If you only read this part
To keep your number when switching: get an MNP reservation number from your current carrier (usually free, takes minutes in their app), then enter it when you sign up with the new carrier. Your number transfers in one to two business days.
The reservation number is valid for about 15 days, and some carriers require a few days of validity remaining when you apply — so request it shortly before you switch, not weeks ahead. Completing the transfer automatically cancels your old plan.
Section 01
What MNP is, in one paragraph.
MNP — Mobile Number Portability — is the system that lets you change Japanese carriers while keeping the same phone number. Without it, switching would mean a new number and the chore of telling everyone. With it, you move from, say, Rakuten to LINEMO and your number comes with you.
The whole process hinges on one thing: a temporary code called the MNP reservation number (MNP予約番号). You get it from the carrier you're leaving, and you hand it to the carrier you're joining. That's the bridge your number walks across.
Section 02
The steps, in order.
Decide where you're going first
Pick your new carrier before you start. Because the reservation number expires, you don't want to get it and then dither. If you're comparing options, our main SIM guide covers the main domestic carriers.
Request the MNP reservation number from your current carrier
This is usually done in the carrier's app or website, sometimes by phone. It's typically free and issued quickly. You'll receive a code (the reservation number) and an expiry date.
Note the expiry and validity requirement
The number is valid for around 15 days. Some new carriers require several days of validity remaining at the time you apply. Plan to sign up with the new carrier within a day or two of getting the number.
Sign up with the new carrier and enter the MNP number
During sign-up, choose the "keep my number / MNP" option and enter your reservation number plus your current phone number. The new carrier handles the rest.
Complete identity verification (eKYC)
As with any new line, you'll verify your identity — usually by photographing your residence card and your face. Good lighting, no hat, no glasses.
Wait for the switch, then set up the new SIM
The transfer usually completes in one to two business days. For an eSIM, you'll get a QR code or activation prompt. For a physical SIM, insert it and configure the APN if needed. There may be a brief gap where the old line stops before the new one starts.
Confirm your number works — you're done
Make a test call and send a text. Your old contract is automatically cancelled by completing the MNP, so there's nothing else to close.
Section 03
Timing pitfalls to avoid.
- Don't request the reservation number too earlyIt expires in about 15 days, and carriers may need validity remaining when you apply. Getting it weeks ahead just means it lapses and you have to request it again.
- Don't start the switch right before something criticalThere can be a short window where neither line is fully active. Avoid porting the morning of an important call or a flight where you need connectivity.
- Settle device installments firstIf you're still paying off a phone on the old carrier, MNP doesn't erase that balance. Check what happens to the installment before you leave.
- Keep your residence card address currentIf the address on file doesn't match your residence card, the new carrier may reject the application — same as any new sign-up.
Section 04
When MNP is and isn't the right move.
Use MNP when: you're switching between Japanese carriers and your number matters — you've given it to your bank, your employer, your landlord, your friends. That's almost everyone after a few months in Japan.
Skip MNP when: you're brand new and your current number is a temporary travel eSIM data line with no real number attached, or you're leaving Japan entirely. MNP moves numbers between Japanese carriers; it doesn't preserve a Japanese number once you've left the country.
If you're switching specifically to save money, our reviews of LINEMO and Rakuten Mobile walk through the cheapest domestic options for foreign residents.
FAQ
Frequently asked questions
What is MNP in Japan?
MNP stands for Mobile Number Portability (in Japanese, ナンバーポータビリティ). It lets you keep your existing phone number when you switch from one Japanese carrier to another. You request a reservation number from your current carrier and use it when signing up with the new one, and your number transfers across.
Is there a fee to keep my number?
In most cases, no. Since regulatory changes, the major Japanese carriers stopped charging MNP transfer-out fees, so moving your number between carriers like LINEMO, povo, ahamo, and Rakuten is generally free. Always confirm with your specific carrier, as edge cases exist.
How long does the MNP reservation number last?
The MNP reservation number is typically valid for 15 days from issue. Many carriers also require a certain number of days of remaining validity when you apply with the new carrier, so don't request it too early — get it shortly before you plan to sign up with the new carrier.
How long does the actual number transfer take?
Usually one to two business days. With some carriers and the newer one-stop MNP system, it can be same-day. During the switch there may be a short window where your old line stops working before the new one activates, so don't start the process right before something time-critical.
Can I keep my number if I'm leaving Japan?
MNP only moves your number between Japanese carriers — it doesn't help you keep a Japanese number after you leave the country. If you're departing Japan, you generally cancel your line. Some services let you hold a Japanese number remotely, but that's separate from standard MNP.
Do I need to cancel my old plan separately after MNP?
No. Completing the MNP transfer automatically cancels your old contract — that's the point of the process. You don't contact the old carrier again to cancel. Just make sure any final bill is settled and any device installment is accounted for.