- Make sure that you have an active plan with your wireless carrier.
- Update your iPhone to the latest version of iOS.
- Go to Settings and turn on airplane mode. Wait about 10 seconds, then turn off Airplane Mode.
- Restart your iPhone. Press and hold the Sleep/Wake button until you see the slider. Drag the slider to turn off your device. Then press and hold the Sleep/Wake button again until you see the Apple logo.
- Check for a carrier settings update. Go to Settings > General > About. If an update is available, you'll see a prompt to select OK or Update.
- Remove your SIM card from the SIM card tray and then put the SIM card back. Make sure that the SIM tray closes completely and isn’t loose. If you use a SIM tray from a different model iPhone or from another phone manufacturer, it might not fit properly.
- Try using another SIM card. If you don't have one, go to your carrier's retail store and ask them to test with another SIM card. You might need to replace your SIM card.
If you still see an alert about your SIM card, contact Apple support.
Learn what to do if you see a SIM not supported alert.