Phone reverting to the home SIM automatically

Check first

Set data back to the KnowRoaming line: Cellular Data on iPhone, Mobile data under Preferred SIMs on Samsung, Mobile data on the SIM's screen on other Android phones. Then confirm Data Roaming is still on for the KnowRoaming line and off for your home SIM. See Use your KnowRoaming plan for data instead of your home SIM.

Causes, in order

Cellular Data Switching is on (iPhone)

iPhone can move data between lines on its own when it thinks the other line is better. This is the most common cause of "I set it to KnowRoaming and it moved back." Turn it off: Settings > Cellular > Cellular Data > Allow Cellular Data Switching.

A restart reset the data line

Some phones return the data line to a default after a restart. Re-select the KnowRoaming line, then check roaming.

A software update reset your preferences

Updates occasionally reset cellular settings. Check the data line and Data Roaming after any update while you're abroad.

Why it matters

If data slips back to your home SIM with its roaming on, you pay your carrier's roaming rate without noticing. With roaming off on the home SIM, as it should be, you notice quickly because data stops. Either way, a five-second check after a restart or update is worth it. Your plan is data only, with no phone number, calls, or SMS. Calls and texts keep using your home number.

Still not working?

Still not working? Message us on WhatsApp at +1-888-357-7347 and include four things: your ICCID, your order number, your phone model and OS version, and what you've already tried.