The "SOS" message at the top of your phone means that your device is not connected to your regular cellular network, so it cannot make normal calls, send texts, or use data through your carrier. However, it can still make emergency calls by connecting through other available networks or satellite emergency services. This usually happens when you're in an area with poor or no coverage from your carrier, the SIM card has issues, roaming is restricted, or there are network problems. Your phone is essentially in a limited connectivity state, allowing only emergency communications.

To fix this, try restarting your phone, toggling Airplane mode on and off, checking for carrier settings updates, reinserting or checking your SIM card, moving to an area with better coverage, or contacting your carrier if the problem persists.