what does SOS mean?

"SOS" or "SOS ONLY" displayed in your iPhone's status bar means your device isn't connected to a network but you are still able to make an SOS emergency call.

It means that your phone has lost its connection with your carrier.

Contact your carrier to work through this.

It means the only calls you can place are Emergency 911 calls ("SOS") – if even those.

USA Today – What does 'SOS' mean? The term's maritime origins and how it shows up in our lives today.