- eSIM versus physical SIM
- What activation involves
- A safe order for changing phones
- Dual SIM and travel abroad
The short answer
An eSIM is a chip built into your phone onto which your carrier writes your contract details over the network. With no card to insert, adding, moving and deleting a line all happen on screen. The moment that needs most care is changing phones: do not wipe the old phone until the new one is confirmed working.
eSIM versus physical SIM
A SIM is your membership card for a carrier's network (see "What is a SIM card?"). An eSIM does exactly the same job; only the container differs. A physical SIM delivers the contract on a card, while an eSIM delivers the same information as data and stores it on a chip inside the phone. That stored bundle of contract information is called a profile.
| Point | Physical SIM | eSIM |
|---|---|---|
| How it arrives | A card by post or over the counter | Written over the network |
| Time to get started | Wait for the card | Can sometimes be set up once the paperwork is done |
| Losing or damaging it | The card can go missing | No card to lose |
| Changing phones | Move the card across | A transfer or reissue is needed |
| Requirement | A phone with a SIM tray | A phone that supports eSIM |
In Japan, the Ministry of Internal Affairs and Communications published guidelines to promote eSIM in August 2021 and asked the major network operators (MNOs) to offer it. Whether a given carrier offers eSIM, and which steps can be done online, still varies from company to company, so check before you sign up.
How activation works
The details differ by carrier, but the broad sequence looks like this.
- Confirm that your phone supports eSIM and is not SIM-locked.
- Apply to the carrier and complete identity verification.
- Follow their instructions to write the profile to the phone, either by scanning a QR code or through the carrier's app.
- Enter APN settings (where the phone connects for data) if required.
- Check that calls, SMS and mobile data each work.
The key thing to have ready is Wi-Fi. Until the profile is installed, you have no mobile connection, so connect to Wi-Fi at home or at work first. If you are activating by QR code, remember that you scan it with the camera of the phone you are setting up, so the code needs to be on another screen, such as a laptop or someone else's phone, or printed on paper.
A QR code may not work a second time. Do not count on reusing one; if something goes wrong, follow your carrier's instructions for getting a new profile.
Changing phones and reissuing
When you need a reissue
With an eSIM, you may need to have the profile written again (a reissue) in situations like these.
- Moving to a new phone
- The phone breaks or is lost
- The phone is reset, or the eSIM profile is deleted by mistake
Carriers accept reissue requests online, by phone or in store, but which channels they offer and whether a fee applies vary. Check your carrier's guidance. Some phones can transfer an eSIM directly from the old handset to the new one, but whether that works depends on the combination of carrier and device.
An order that avoids trouble
Say you use your phone for work and plan to switch handsets over a weekend. This order keeps problems to a minimum.
- Back up the old phone.
- Check that the new phone supports eSIM and the frequency bands your network uses.
- Set up the eSIM on the new phone and confirm that calls, SMS and data all work.
- Move your authenticator app (the app that generates login codes) and sign in to your services.
- Only then reset the old phone.
Reset the old phone before confirming the new one works and the profile may be gone, leaving a gap where your number works on neither phone. During that gap, SMS login codes will not arrive either.
Take particular care if your online bank or other services send login codes by SMS. If a login is required partway through the switch, the code has nowhere to go while your SIM is inactive. Start when you have time to spare and when your carrier's support lines are open.
Dual SIM: two lines in one phone
Dual SIM lets a single phone use two lines. The combinations, such as one physical SIM plus one eSIM, or two eSIMs, depend on the model.
Some ways people use it:
- Keeping a work number and a personal number on one phone
- Using your existing line for calls and a different carrier for data
- Switching to the other line where one has weak coverage
There are things to decide. You need to set which line handles data and which number is used for outgoing calls. Whether both lines can receive calls at the same time, and what happens to one while the other is on a call, differs by phone. And naturally, you pay for both lines.
Using it abroad
Using your home contract in another country is called data roaming: your carrier lets you connect through a partner network overseas. Charges vary by carrier, plan and destination and can become expensive depending on how you use the phone, so check before you travel. Turning data roaming off in Settings prevents unintended use.
Another option is to add a data-only eSIM for use at your destination. This is a form of dual SIM: your home line stays active for calls and texts, and data goes through the added eSIM. Even then, if data roaming is still on for your home line, the phone may use it, so check the settings. It is also worth checking what your carrier charges for incoming calls and texts while abroad.
Using a foreign SIM or eSIM requires a phone that is not SIM-locked. In Japan, phones released before October 2021 may still carry a lock, so check that first.
In summary
An eSIM is the same membership card as a physical SIM, delivered as data rather than plastic. Without a card to swap, changing phones or resetting one requires a deliberate step.
- Activate while connected to Wi-Fi, with the QR code on a separate screen.
- When changing phones, confirm the new one works before resetting the old one.
- Check your carrier's guidance on reissue channels, fees, and direct transfers between phones.
- With dual SIM or travel, decide in Settings which line carries your data.