Which Line Is Using Your Data
Confirm your travel plan is carrying traffic, not your expensive home line.
Which Line Is Using Your Data
The costly mistake abroad is having a Simsima plan installed and working while the device quietly routes data through your home line.
Check on iPhone
Settings > Cellular. Under Cellular Data, the selected line is the one carrying traffic. Below, usage is broken down per line so you can see which has actually been consuming.
Turn off automatic switching. Settings > Cellular > Cellular Data > Allow Cellular Data Switching. Left on, iOS falls back to your home line whenever the eSIM signal dips — silently, and at your carrier's roaming rates.
Check on Android
Settings > Network & internet > SIMs > Mobile data, and confirm your Simsima plan is selected. Per-line usage sits under App data usage.
Samsung: Settings > Connections > SIM manager > Mobile data.
The Extra-Safe Approach
Turn data roaming off on your home line entirely. It can then still receive calls if it stays registered, but it cannot carry data whatever the device decides. See avoiding roaming charges.
Giving each line a clear name first makes all of these screens much easier to read.
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