How to Choose Which SIM Uses Mobile Data on Samsung

Samsung phones manage physical SIMs and eSIMs through SIM Manager. Selecting the travel eSIM under Mobile Data tells the phone which line should provide internet access; it does not move the telephone number from the primary SIM.

Quick answer: Open Settings → Connections → SIM Manager → Mobile Data and select the travel eSIM. Turn off Data Switching or Backup Calling if it could return data to the primary line, enable Data Roaming only on the travel eSIM when required and keep roaming off on the home SIM.

Open SIM Manager and identify both lines

Go to Settings, choose Connections and open SIM Manager. Depending on the Samsung model and One UI version, the menu may be called SIM card manager. Both installed lines should appear with an on/off control.

Rename the lines before making changes. Labels such as “Home” and “Travel” are safer than SIM 1 and eSIM 1, especially when the phone asks which line should handle data, calls or messages.

Select the travel eSIM for Mobile Data

Open Settings.
Tap Connections.
Open SIM Manager.
Make sure the travel eSIM is switched on.
Tap Mobile Data or Preferred SIMs → Mobile data.
Select the travel eSIM.

The wording can vary by country, carrier and One UI version. If no Mobile Data choice appears, check whether the second line is enabled and whether the device supports dual-SIM operation in its current configuration.

Stop automatic switching to the home SIM

Some Samsung phones include Data Switching, Auto Data Switching or Backup Calling. When enabled, the phone may use the other SIM if the selected data line loses service. That can be helpful at home but can create roaming charges abroad.

Turn the feature off when the primary SIM must not provide mobile data. The exact control may appear inside SIM Manager or under the primary data-line settings. Recheck after an operating-system update because menu locations can change.

Apply roaming to the correct line

A travel eSIM may need Data Roaming because it connects through a local partner network. Enable roaming for the travel eSIM when the plan instructions require it. Keep Data Roaming disabled on the primary SIM unless you have deliberately accepted the home carrier’s charges.

On some Samsung versions, Data Roaming appears under Connections → Mobile networks rather than inside each SIM card. Confirm which line is selected for mobile data before changing that control.

Keep the primary number available

The home SIM can remain enabled for its number, incoming SMS or calls while the travel eSIM handles data. Ordinary calls, voicemail and SMS still follow the home carrier’s international pricing, even when mobile data uses the travel line.

NoveSIM travel eSIMs are data-only. WhatsApp, maps, email and internet calling use the selected data connection, while the normal telephone number remains with the primary carrier.

Test the selection without Wi-Fi

Turn off Wi-Fi temporarily, open a normal webpage and check that the Mobile Data indicator appears on the travel line. You can also open Settings → Connections → Data usage and confirm which SIM’s counter increases.

If there is no connection, verify that the plan covers the current country and is active. Leave Network Selection on Automatic. If a NoveSIM plan requires manual APN entry, use data.esim and leave username and password blank.

If Samsung keeps using the wrong SIM

Confirm that the travel eSIM is still selected under Mobile Data.
Disable Data Switching or Backup Calling.
Turn off Data Roaming on the primary SIM.
Toggle Airplane Mode once to refresh registration.
Restart the phone if the menu does not retain the selection.
Check for a carrier app or work profile that manages SIM settings.

Do not delete the travel eSIM. If the settings keep reverting, record the exact Samsung model and One UI version before contacting support.

FAQ

Where is SIM Manager on a Samsung phone?

On most recent models it is under Settings → Connections → SIM Manager. The name and available controls can vary by One UI version, carrier and region.

Can one Samsung SIM handle calls while another handles data?

Yes, on supported dual-SIM models. Choose the travel eSIM for Mobile Data and leave the primary SIM selected for calls or messages if required.

Why does my Samsung switch mobile data back to the home SIM?

Data Switching, Auto Data Switching or Backup Calling may be enabled. Turn that feature off and confirm the preferred data SIM again.

Should Data Roaming be on for both SIMs?

No. Enable it on the travel eSIM only when the plan requires it. Keep roaming off on the home SIM unless its international tariff is understood and accepted.

Final Recommendation

Use Samsung SIM Manager to give each line a clear role: the travel eSIM for Mobile Data and the primary SIM for its existing number when needed. Disable automatic data switching before travelling.

After arrival, enable the required roaming setting only on the travel line and test away from Wi-Fi. This confirms the selected SIM is supplying data without exposing the home line to accidental roaming.