To check which SIM is used for mobile data on a dual-SIM phone, open the dedicated Cellular, Mobile Network or SIM Manager setting. Signal bars alone do not identify the active data line.
This matters when using a travel eSIM: the home SIM can remain available for its number while the eSIM handles internet traffic.
NoveSIM travel eSIMs are data-only. Ordinary calls and SMS remain with the line that owns the telephone number.
Quick answer: On iPhone, open Settings → Cellular/Mobile Service → Cellular Data. On Android, open Settings → Network & Internet/Connections → SIMs/SIM Manager → Mobile Data. Select the travel eSIM and disable automatic data switching.
How to Check Which SIM Is Used for Mobile Data on iPhone
- Open Settings.
- Tap Cellular or Mobile Service.
- Tap Cellular Data.
- Select the labelled travel eSIM.
- Turn off Allow Cellular Data Switching when preventing home-SIM data use.
Menu wording can vary by iOS version and region. The checkmark beside a line identifies the current data SIM.
Check the Mobile-Data SIM on Android
- Open Settings.
- Choose Network & Internet or Connections.
- Open SIMs or SIM Manager.
- Under Mobile Data, select the travel eSIM.
- Disable automatic or backup data switching.
Samsung, Pixel and other manufacturers use different labels. The Android eSIM guide provides additional menu context.
Verify That the Selected SIM Is Working
Turn off Wi-Fi, load a normal webpage and check the data indicator beside the intended line. Enable Data Roaming on the travel eSIM when its instructions require it, while keeping roaming off on the primary SIM.
See the Data Roaming guide before changing both lines.
If the Phone Keeps Switching Back
Disable automatic data switching, confirm the travel plan is active and restart the phone. If manual APN entry is required, use data.esim. Do not delete the eSIM unless Support instructs you.
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FAQ
How do I know which SIM is using data?
Open the phone’s Mobile Data setting; the selected or checked line is the active data SIM.
Can both SIMs use mobile data simultaneously?
Most phones select one data line at a time, although automatic switching may move between them.
Can I keep the home SIM active?
Yes, but keep its Data Roaming off and review charges for calls, SMS and voicemail.
Should Data Roaming be on for the travel eSIM?
Enable it when the plan instructions require it; keep it off on the home SIM.
Final Recommendation
Check which SIM is used for mobile data in the dedicated setting rather than relying on signal bars.
Choose the travel eSIM, disable automatic switching and test with Wi-Fi off.
Keep the home line available only under settings that prevent accidental roaming data.
