This is the step most people get wrong, and the roaming bill afterwards is an unpleasant surprise.
What the problem actually is
When you go abroad, your home SIM still latches onto a local network. Three things can be billed:
- Data roaming — the expensive one, and the cause of the horror-story bills.
- Roaming calls — expensive, but only when you make or take one.
- Receiving SMS — usually free or very cheap.
The goal: kill the first, keep the third.
On iPhone
- Settings → Cellular
- Select your home SIM
- Turn off "Cellular Data" for that line
- Open "Cellular Data Options" → turn off "Data Roaming"
- Go back, select the travel eSIM → turn on cellular data for it
- Under "Cellular Data" at the top, choose the travel eSIM as the data line
Then check: the status bar should show the foreign operator with a data symbol, and your home SIM should still show bars.
On Android
The path differs by manufacturer, but the idea is identical:
- Settings → Network & internet → SIMs
- Select your home SIM → turn off "Roaming"
- Select the travel eSIM → turn on mobile data
- In the default-SIM-for-data setting, choose the travel eSIM
Check before you fly
Do not discover a wrong setting after you land. Before flying, switch the eSIM on briefly and confirm:
- The status bar shows both lines.
- "Cellular Data" points at the eSIM.
- Data roaming is off for your home SIM.
What about bank verification codes
This is the most common question, and the answer depends on your bank:
- Sent by SMS: you still receive them, because your home SIM is still registered on a network. Some operators charge a small fee for receiving messages abroad.
- Sent through the bank's app: needs data — which will run over the travel eSIM. Works normally.
- Delivered by automated phone call: that is a roaming call and will be billed. If your bank uses this, consider switching method before you travel.
One thing worth doing
Before you fly, open your banking app and check how it verifies you. Knowing in advance beats finding out while trying to make an urgent transfer abroad.