Steps to Fix :

• When connecting to the AT&T network, you'll need a SIM card to enjoy cellular services.
• Find the SIM tray.-The SIM tray is positioned on the device's right side. To enter a SIM card, eject the SIM tray by inserting a SIM tool into the tiny hole.
•  Replace or delete the SIM card-With the gold contacts facing up and the notched edge on the upper left, insert or remove the Nano-SIM card into the SIM tray. Reinstall the SIM tray until it clicks into place and is flush with the device's side.
• If there isn't a SIM card in the device, the Control Center will say 'No SIM.'

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