Symptoms
- Only one SIM works for calls or data at a time
- Can't choose which line sends a text or makes a call
- One SIM shows no service while the other works fine
- Data won't work on the second line even though it should
Likely causes
- CommonDefault line settings not configured correctlyPhones need explicit settings for which SIM handles calls, texts, and data by default.
- CommonOne SIM/eSIM not properly activated or provisionedA dual SIM setup only works if both lines are actually active with their carriers.
- PossiblePhone or carrier limitation on simultaneous data useSome dual SIM setups only allow one line to use data at a time (not both simultaneously).
- PossiblePhysical SIM and eSIM conflict in a hybrid setupSome phones require choosing between using two physical SIMs or one SIM plus an eSIM, not all three.
- Less commonCarrier-specific restrictions on dual SIM/eSIM useA few carriers don't fully support dual SIM configurations.
What to do
- Go into the phone's SIM management settings and confirm both lines show as active.
- Set clear defaults for which line handles calls, texts, and data, or choose 'ask every time' if you want manual control.
- Confirm both lines are properly activated with their respective carriers.
- Check whether your phone model supports simultaneous data on both lines or only one at a time, which is a common hardware limitation.
- Restart the phone after making SIM setting changes.
- Contact each carrier to confirm their service supports being used in a dual SIM configuration.
When to call a pro
If one line consistently fails to work in dual SIM mode despite correct settings, contact that carrier to confirm their service supports dual SIM phones.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.