The first step in unlocking a locked phone is to determine whether you are in an area with good cellular reception. You can also enable/disable airplane mode, reboot the phone, and ensure that your SIM card is in place. This is typically displayed when the phone cannot connect to your cellular carrier's network. Resetting network settings may be necessary to restore network service if the problem persists.
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https://devicefixes.com/blog/how-to-get-phone-out-of-sos-mode/
