Last updated: July 25, 2026
Before a trip abroad, a lot of people wonder whether they can simply leave their b-mobile (Nihon Tsushin) SIM as it is. Two worries come up most often: data being used over a foreign network without you noticing, and what happens to your Japanese phone number while you're away. The short answer is that it's easiest to travel with data roaming switched off on your b-mobile line and cover your internet abroad with an eSIM — the setup stays simple, and it's easy to see what's actually connected. This guide walks through where the settings live on iPhone and Android, how to choose which line carries your data when you're running an eSIM alongside your regular SIM, what happens to your number and SMS, and what to check before you fly. It focuses on settings only, so if you also want the bigger picture for a specific destination, see the overview article as well.
- Why roaming off is the default abroad
- Where the settings are on iPhone and Android
- How to pick the data line when using an eSIM
- What happens to your number and SMS
- What to check if you can't get online
The basic setup abroad: b-mobile data off, internet on the eSIM
There are several ways to handle your phone overseas, but the clearest one for a first trip is this: stop data on the line you use in Japan, and get your connectivity abroad from an eSIM. The reason is simple — you can tell at a glance which line is doing the work.
As long as your phone is on, it can use data on its own: app updates, cloud sync, background refresh. With roaming switched off on your Japanese line, that traffic is far less likely to end up on a foreign network. Leave it on, and depending on where you go and what your plan covers, you may end up with connections you didn't plan for.
For the wider picture — what options b-mobile users have abroad, how to think about cost, and what to do before and after the trip — see Travelling abroad with a b-mobile SIM: solving mobile data with an eSIM. This article zooms in on the pre-departure settings part of that story.
What actually changes when data roaming is off
Data roaming is the setting that lets your phone use mobile data outside your carrier's own network — on partner networks abroad, for example. Turn it off and your phone won't use data over those foreign networks.
- Unplanned traffic — automatic app updates, photo backups — is much less likely to happen
- Your data runs through the eSIM, so tracking what you've used is straightforward
- You don't need to dig into the roaming terms for every country you visit to know where you stand
Roaming availability, covered countries and charges differ by carrier and plan, and they change over time. Check Nihon Tsushin's official information for what applies to your own contract (accurate as of July 2026). This article doesn't state specific prices or conditions.
Comparing the three common setups
Here are the three approaches side by side. For most trips and short stays, the first row is the easiest to live with.
| Setup | Internet access | Your Japanese number | Watch out for |
|---|---|---|---|
| b-mobile SIM = data roaming OFF + eSIM = ON | Works via the eSIM | Line stays active (calls and texts to the number aren't usable) | You need to switch the mobile data line over to the eSIM |
| b-mobile line turned off entirely + eSIM = ON | Works via the eSIM | Shows as out of service | Easy to forget to turn the line back on when you get home |
| Airplane mode the whole trip | Only where there's Wi-Fi | Not usable | No maps or translation while you're out and about |
Setting it up on iPhone
1. Turn off data roaming on the b-mobile line
Go to Settings → Cellular (Mobile Data) → select your b-mobile line from the list → switch off Data Roaming. Giving each line a label (for example "Japan number" and "Travel") makes it much clearer which one you're changing.
2. Add your eSIM
With Bloomy eSIM, you tap the setup link you receive once and follow the on-screen prompts. It's worth doing this while you're still home and have a stable connection, rather than at the airport. If the tap-to-install route doesn't go through, manual installation is also available. Step-by-step instructions with screenshots are on our setup guide.
3. Switch your data line after you land
Go to Settings → Cellular (Mobile Data) → Cellular Data (Mobile Data) and choose the eSIM as the line used for data. While you're there, check that the eSIM line itself is switched on. Activation timing can differ between plans, so read the information you get at purchase too.
Setting it up on Android
Menu names vary a little between manufacturers, but the path is broadly the same.
- Open Settings → Network & internet → SIMs or Mobile network
- Select the b-mobile line and switch Roaming off
- Add the eSIM, then set it as the line used for Mobile data
- Check that the APN has been configured automatically, if needed
Whether your handset supports eSIM depends on the model and when it was released. Checking our compatible devices page before you travel saves a scramble on the day.
What happens to your Japanese number and SMS
Turning off data roaming doesn't cancel anything — your contract stays as it is. Whether you can actually make calls or receive SMS on that number while abroad depends on the international roaming terms of your plan. If you're counting on using the number or receiving texts overseas, check Nihon Tsushin's official information before you leave. This is the kind of detail that changes, so we won't state it definitively here.
To be straightforward about Bloomy eSIM as well: it is data-only. There is no phone number, and no voice calls or SMS. App-based calling that runs over data — WhatsApp, Messenger, FaceTime and the like — works as normal. What you can't do is make or receive calls on a phone number, or send and receive SMS. If you regularly need the number itself — SMS verification codes from a bank or another service, for instance — it's worth deciding in advance how you'll handle your Japanese line, or arranging a separate option that includes a number.
Who this setup suits — and who needs something more
In short: it works well for trips and short stays where your data use is fairly predictable, and it needs supplementing if you rely on a phone number day to day.
A good fit if you
- Are away for a few days to a few weeks and mainly need maps, translation and social apps
- Want your connectivity costs to be easy to understand
- Are happy for your Japanese number to simply sit there unused
Not a good fit — or needs a second option — if you
- Need to receive SMS verification codes on your Japanese number while you're away
- Expect to take calls on a local number (look into a local SIM or another option that includes a number)
- Have a handset that doesn't support eSIM
If you can't get online after you arrive
Work down this list — most problems turn out to be one setting.
- Is airplane mode still on?
- Is the eSIM line switched on?
- Is the eSIM selected as the line for mobile data?
- Is data roaming switched on for the eSIM line? (Some plans need it to connect to the local network.)
- Restart the phone, and set network selection back to automatic
If that doesn't fix it, there's more detail on our connection troubleshooting page, and common questions from before and after purchase are on the FAQ. It also helps to know in advance that speed and stability can vary with the local network, the area you're in, your device, and how busy the network is at the time.
Your pre-departure checklist
There isn't much to it. 1) Check that your phone supports eSIM. 2) Turn off data roaming on your b-mobile line. 3) Install the eSIM before you leave. 4) Switch your data line to the eSIM once you arrive. Cover those four and you'll have maps and messaging working from the moment you land.
To look at plans for where you're heading, our eSIM comparison page lets you search by country, data allowance and number of days. Prices and plan conditions can change, so please confirm the current details shown at the time of purchase.
Note: this article describes general setup steps as of July 2026. Menu names differ between OS versions and handsets, and carrier terms can change — check the official information for your own contract. Bloomy eSIM plans are data-only (no phone number, voice calls or SMS); unlimited-type plans are subject to a fair use policy; and connection speed and stability vary depending on the local network, your device, and your location.
