What is data roaming?
Data roaming is using mobile data on a network that is not your own. Here is what it costs, and why a travel eSIM needs it switched on while your home line needs it off.
Data roaming is using mobile data on a network that is not your home operator's. Your phone connects to a local network abroad, that network bills your operator, and your operator bills you.
It is also the switch in your settings that causes the most confusion when you travel with an eSIM, because the right answer is different for your two lines.
Why it costs what it costs
Your operator has no network in the country you are visiting, so it buys access from one that does. The wholesale price it pays is nothing like the retail price you are charged, and the gap is why a few hours of ordinary phone use can produce a bill larger than the flight.
How bad it gets depends entirely on where you are:
- Inside the European Union, roaming is capped by law for EU operators, and in practice it is usually included in your plan. The rules were extended in 2022 and run to 2032.
- Outside it, there is no cap unless your operator chose to set one. This is where the stories come from.
Post Brexit, UK operators are no longer bound by the EU rules, and several reintroduced daily charges for European travel. Check your own plan rather than assuming, because the four UK networks made different choices.
The switch, and the trap
On your phone, data roaming is a per line setting. That is the part people miss.
With a travel eSIM installed you have two lines, and they need opposite settings:
- Your home line: data roaming OFF. This is what stops it quietly connecting abroad and charging you. Keep calls and texts if you want them, turn off its data.
- The travel eSIM: data roaming ON. This feels wrong and it is correct. A travel eSIM is not a local subscription: it rides on partner networks in the country you are in, so from the phone's point of view it is roaming. With the switch off, it has no data at all.
Then set the travel eSIM as the line for cellular data, so the phone actually uses it.
This single setting is behind most "my eSIM does not work" messages. Full signal, correct profile installed, no internet, because data roaming was left off on the line that needed it.
Where to find it
On iPhone: Settings, Cellular, tap the line, then Data Roaming. Do it once per line.
On Android: Settings, Connections or Network, Mobile networks, then Data roaming, choosing the right SIM first.
Quick answers
Should data roaming be on or off for a travel eSIM?
On, for that line. A travel eSIM connects through partner networks, so the phone treats it as roaming. Leave it off and the eSIM will show signal but carry no data.
Will turning roaming on for my eSIM cost me anything on my normal number?
No, as long as you set it per line. The switch belongs to the line you set it on, so your home line stays off while the eSIM is on.
Is roaming free in Europe?
For EU operators travelling inside the EU, it is capped by law and usually included. For operators outside the EU, including UK ones since Brexit, there is no such guarantee and several charge a daily fee.
Why did I get a bill when I never used my phone?
Background data. Apps sync, email refreshes and the operating system updates without you opening anything. Switching data roaming off on the home line is what prevents it, not simply not using the phone.