If your phone displays a 'No Service' or 'Searching' message, it means your device can't connect to a cellular network. Here are possible solutions:
Check Coverage
Make sure you're in an area with network coverage from your provider.
Restart Phone
Restart your phone to fix temporary glitches.
Disable Airplane Mode
Ensure Airplane Mode is off, as it disables all wireless connections.
Check SIM card
Verify that your SIM card is properly inserted and not damaged.
Update Carrier Settings
Install carrier settings updates from Settings > General > About.
Reset Network Settings
This can help, but it removes saved networks and pairings.
Update software
Check for software updates in Settings > General > Software Update.