• A simple setting adjustment, such as Airplane Mode or carrier settings, can cause service outages. In some circumstances, your iPhone's cellular settings must be modified via a software update from your cellular service provider. The SIM card on your phone has to be reset or replaced less frequently. It's also conceivable that your cellular service plan is malfunctioning.
• Cellular and Wi-Fi services are turned off in Airplane Mode. If you notice an aeroplane icon in the upper-right corner of the iPhone screen, where the signal strength bars usually display, the phone is in Airplane Mode.
• Switching your cellular service off and on again will sometimes solve the problem, especially if you are on the edge of a service area or have lost connection and should be back in service. Make sure Cellular Data is turned on in Settings > Cellular. Toggle it off and back on if it's on.

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