Turn data roaming on for the travel eSIM line, and off for your home line. That single combination is the correct setup for almost every traveller, and it is set per line rather than for the whole phone, so both states can be true at once.
The reason people get it backwards is that everything they have ever read about roaming says to switch it off. That advice is about your home line, where roaming means your own provider billing you for using a foreign network. A travel eSIM is the other case: it connects you as a visitor on a local network, so your phone classifies it as roaming, and denying that permission leaves you with signal bars and no internet on a plan you already paid for.
In this guide:
- Should data roaming be on or off with a travel eSIM?
- Why the travel line needs roaming switched on
- Why your home line needs it switched off
- Where the setting lives on iPhone and Android
- The setting almost nobody knows about
- What still works with your home data roaming off
- If you switched it on and still have no data
- The two line configuration at a glance
Should data roaming be on or off with a travel eSIM?
On, for the travel line. Off, for your home line. Nothing else about the setting is complicated once you see that it is a permission rather than a purchase.
The toggle answers one question for one line: may this line use a network that is not its own? For a prepaid travel plan the answer has to be yes, because using a local network is the entire product. For your home line the answer while abroad should be no, because that is where the money is.
Because the toggle is per line, there is no conflict. Your travel line roams; your home line does not; both sit in the phone at the same time.
Why the travel line needs roaming switched on
A travel plan does not build its own towers. It gets you access to local networks in the country you are visiting, and your phone sees any network that is not the line’s home network as roaming. That is a technical classification, not a billing event.
This is why the symptom is so distinctive. With roaming denied, the line still finds a network, so the status bar looks healthy: bars, a network name, a 4G or 5G indicator. What is missing is permission to pass traffic. Everything looks connected and nothing loads.
If that is what you are seeing right now, this is the first thing to check, before restarting anything. Our guide to an eSIM installed but showing no data works through the rest of the sequence, and an eSIM with bars but no internet covers manual network selection when the toggle is not the culprit.
Why your home line needs it switched off
Your home line is the one that can generate a bill, and it does not need a person to use it. Apps refresh in the background, photo libraries try to sync, an operating system checks for updates. Left roaming, a phone in your pocket can accumulate charges while you are asleep.
The key point is that switching data roaming off is not the same as switching the line off. Keep the line enabled. It stays registered for calls and texts, which is exactly what you want: your usual number keeps ringing, and bank verification codes still arrive. Our guide to bank codes and SMS abroad covers why that distinction matters more than any other setting on the phone.
Airplane mode is the blunt version of this and takes the codes with it. Our explainer on what airplane mode actually does covers when it is the right tool and when it is not.
Where the setting lives on iPhone and Android
The wording differs; the setting is the same.
On iPhone. Settings, then Cellular or Mobile Data. Tap the specific line, then Data Roaming. Do this once for the travel line, setting it on, and once for the home line, setting it off. Then go back to the Cellular screen and set Cellular Data, the line that carries data, to the travel line.
On Android. Settings, then Network and internet, then SIMs or Mobile network. Select the line, then look for Roaming or Mobile data roaming. Samsung devices usually place the same controls under Connections, then SIM manager or Mobile networks. As on iPhone, there is a separate setting for which line is the default for mobile data.
Two habits make this much less error prone. Rename each line in settings so that Travel and Home appear instead of two similar default names. And do the whole configuration at home before you fly, so the only thing left at the airport is turning the travel line on.
The setting almost nobody knows about
On iPhone there is a setting called Allow Cellular Data Switching, sitting under the mobile data options. It lets the phone temporarily borrow the other line’s data when it needs to, most visibly during a voice call.
At home, that is a useful convenience. Abroad, the other line is your home line, and borrowing means roaming on your own provider’s terms. It is one of the very few ways to accumulate charges after you have diligently switched off data roaming on the home line, which makes it disproportionately worth finding.
Turn it off while you travel. Turn it back on when you get home if you like it. Our dual SIM travel setup guide covers this alongside the rest of the two line configuration.
What still works with your home data roaming off
Quite a lot, which is why this configuration is comfortable rather than restrictive.
| Function | Works with home data roaming off? |
|---|---|
| Incoming calls to your home number | Yes, as long as the line is on |
| Incoming SMS, including bank codes | Yes, as long as the line is on |
| Outgoing calls on your home number | Yes, and usually charged at roaming call rates |
| WhatsApp, Signal and other messaging apps | Yes, over the travel line’s data |
| Maps, browsing, email, ride hailing | Yes, over the travel line’s data |
| Background app refresh on the home line | No, which is the point |
| Voicemail retrieval | Usually, and often billed as a call |
The pattern is straightforward: your home line handles the things that follow your number, and the travel line handles everything that consumes data. Our guide to keeping your number reachable abroad covers the messaging side in detail.
If you switched it on and still have no data
Work through these in order. Most cases resolve in the first three.
- Check the data line, not just the roaming toggle. Roaming on and the wrong line selected for mobile data is the second most common cause of no connection.
- Give it a few minutes. First registration on a foreign network is not instant, particularly at a busy airport where thousands of handsets are doing the same thing.
- Toggle airplane mode on and off. This forces a fresh network search, and it fixes more arrivals than any other single action.
- Select a network manually. Turn off automatic selection and pick one of the local networks from the list. If the first choice does not connect, try the next.
- Confirm the plan covers the country you are in. A plan only works in the countries on its coverage list, which our guide to Europe plan coverage explains for the most confusing region.
- Check the plan has started and has data left. Our guide to checking how much data is left covers where to look.
If none of that works, support can see the state of your plan from your order details, which is faster than guessing.
The two line configuration at a glance
| Setting | Travel eSIM line | Home line |
|---|---|---|
| Line enabled | On | On |
| Data roaming | On | Off |
| Selected for mobile data | Yes | No |
| Selected for calls and texts | No | Yes |
| Cellular data switching, iPhone | Off while travelling | Off while travelling |
Set it once at home, and the only thing you do on arrival is confirm the travel line is carrying data. Plans for individual countries and regions sit on the destinations page, and a first time walkthrough of the whole process, from purchase to first connection, is in our installation and activation guide. If you have not bought yet, Viasimo delivers plans by email as a one off prepaid purchase.
