When running multiple SIMs, your phone needs to know which one should handle mobile data. Setting the correct default data line is critical for travel eSIM users who want all internet traffic routed through the travel plan instead of through the home carrier at roaming rates. This guide covers the data line configuration on every major platform.
Step-by-step instructions
- 1
Set the data line on iPhone
Go to Settings > Cellular > Cellular Data. You will see a list of all active SIM lines. Tap the eSIM line to select it as the data source.
All internet traffic (browsing, apps, streaming, background updates) now routes through this line. The change takes effect immediately. Also turn off 'Allow Cellular Data Switching' below the SIM selection to prevent fallback to the other line.
Tip: When you change the data line, all active connections reset. Any ongoing downloads or streaming sessions restart on the new line.
- 2
Set the data line on Samsung
Go to Settings > Connections > SIM Manager. Tap 'Mobile data' and select the eSIM from the list. Samsung confirms the selection and switches data immediately.
You can also quickly switch data lines from the notification shade by pulling down and tapping the SIM toggle tile (if added to Quick Settings).
Tip: Samsung has a 'Data switching' option in SIM Manager that allows automatic fallback to the other SIM when signal is lost. Disable this for travel to avoid roaming charges on your home SIM.
- 3
Set the data line on Pixel
Go to Settings > Network & internet > SIMs. Tap the eSIM profile. Tap 'Use for data' or toggle on 'Mobile data.' Pixel switches the data line immediately and shows a notification confirming the change.
All subsequent internet traffic routes through the selected eSIM.
Tip: Pixel displays a small arrow icon next to the SIM using data in the Network & internet menu, making it clear which line is currently handling traffic.
- 4
Verify the change and check data usage
Turn off Wi-Fi and open a browser to confirm pages load over mobile data. Then check that usage is tracking against the correct line: on iPhone, go to Settings > Cellular and scroll to the per-app data section under the eSIM line. On Android, go to Settings > Network & internet > Data usage > select the eSIM to view its usage graph.
If usage appears under the wrong line, repeat the data line selection step and restart the phone.
Tip: Checking data usage after the switch confirms the change stuck. A quick 5MB test load is enough to register in the usage counter within a minute.
Frequently asked questions
Does changing the data line affect calls and texts?
No. Calls, texts, and data are assigned independently. Changing the data SIM does not change which SIM handles calls or SMS. You can have calls on your physical SIM and data on your eSIM without any interference.
Can I route specific apps through a different SIM?
Stock iOS and Android do not support per-app SIM routing. All apps use whichever SIM is set as the default data line. Some third-party apps on Android can route through VPN configurations that you could theoretically bind to a specific interface, but this is not a standard consumer feature.
Why is data still using my old SIM after I changed the setting?
Toggle Airplane Mode on and off after changing the data line. Some phones need a radio reset to switch the data path. If the issue persists, restart your phone. Also verify that 'Allow Cellular Data Switching' (iPhone) or 'Data switching' (Samsung) is turned off, as this feature can override your selection.
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