Quick Answer: MNP (Mobile Number Portability) lets you switch carriers while keeping your phone number. Since 2021, MNP transfer fees are ¥0. The process: get an MNP reservation number from your current carrier, apply at the new carrier within 15 days, activate the new SIM, and your old contract automatically terminates.
What Is MNP?
MNP (Mobile Number Portability / 携帯電話番号ポータビリティ) is the system that allows you to transfer your phone number from one carrier to another. In Japan, this has been available since 2006, and since 2021, all transfer fees have been abolished — making switching completely free.
Step-by-Step MNP Process
Step 1: Get Your MNP Reservation Number (MNP予約番号)
Contact your current carrier to request an MNP reservation number. This is a 10-digit code that authorizes the transfer:
| Current Carrier | How to Get MNP Number |
|---|---|
| docomo | My docomo website, phone (151), or docomo shop |
| au / povo | My au website, phone (0077-75470), or au shop |
| SoftBank / LINEMO | My SoftBank website, phone (*5533), or SoftBank shop |
| ahamo | ahamo website (online only) |
| Rakuten Mobile | my Rakuten Mobile website or app |
| MVNOs (IIJmio, mineo, etc.) | Each carrier's member portal (check their support page) |
Tip: Getting the MNP number online is faster and avoids retention pitches from store staff.
Step 2: Apply at Your New Carrier Within 15 Days
The MNP reservation number is valid for 15 days. When applying at the new carrier, select "MNP transfer" (のりかえ / MNP) instead of "new number." Enter your MNP reservation number during the application. Most carriers recommend applying with at least 7+ days remaining on the reservation to allow processing time.
Step 3: Receive and Activate the New SIM
Once you receive your new SIM (or eSIM QR code), follow the activation instructions. Upon activation:
- Your new SIM becomes active with your existing phone number
- Your old SIM automatically deactivates
- Your old carrier contract is automatically terminated
- There is typically a brief period (minutes to a few hours) where your phone may not work during the switchover
Step 4: Configure Your New SIM
Insert the new SIM card (or scan the eSIM QR code), configure APN settings if required, and restart your phone. Test a call and data connection to confirm everything works.
Timing Tips
- Switch near the end of your billing cycle — Most carriers charge the full month's fee even if you leave mid-month. Switching in the last few days minimizes overlap billing.
- New carrier may offer first-month prorating — Some carriers prorate the first month, others charge the full amount. Check with the new carrier.
- Avoid switching on weekends/holidays — Some activation processes require business-hours support if issues arise.
What Happens to Your Carrier Email?
If you used a carrier email address (@docomo.ne.jp, @ezweb.ne.jp, @softbank.ne.jp), you will lose access to it after switching — unless you pay the "email retention" service (¥330/month at most carriers). Consider migrating important accounts to a personal email (Gmail, etc.) before switching.
MNP "One-Stop" System (ワンストップ方式)
Since 2023, Japan introduced the MNP One-Stop system for major carriers. With this system, you can complete the entire transfer at the new carrier's website without separately contacting your old carrier for an MNP number. The new carrier handles the transfer request directly. This is currently supported between major carriers and sub-brands but may not be available for all MVNOs.
Q: Is there any fee for MNP transfer?
No. Since April 2021, all MNP transfer fees have been abolished. Both the outgoing and incoming carriers charge ¥0 for the transfer itself. You will still pay the new carrier's regular plan fees.
Q: Can I port my number from a prepaid/tourist SIM?
It depends on the prepaid SIM. Some prepaid voice SIMs support MNP; data-only SIMs do not have a phone number to port. Check with your prepaid SIM provider.
Q: What if my MNP reservation number expires?
Simply request a new one from your current carrier. Requesting an MNP number does not cancel your current contract — it only becomes effective when you actually activate a new SIM at another carrier.
Disclaimer: MNP processes may vary slightly by carrier. The One-Stop system is not universally available for all carriers. Please confirm the latest process on your current and new carrier's official websites.
