The "SOS only" mode on a phone means it is connected to a cellular network that allows emergency calls only, but it cannot connect to the usual carrier network for regular calls or data. This usually happens when your phone loses connection to your carrier but can still make emergency calls. Common causes of "SOS only" mode include:

• SIM card issues: The SIM card might be damaged, inactive, or not properly inserted.
• Weak or no network signal: Being in an area with poor cellular coverage like basements, thick-walled buildings, or remote locations.
• Software bugs or outdated iOS: Network connectivity issues can arise from iOS glitches or older software versions.
• Outdated carrier settings: Sometimes carrier settings updates are needed to restore normal network access.
• eSIM configuration errors: Incorrect or expired eSIM profiles can cause this issue.
• Hardware faults: Damage to the phone’s antenna or network hardware.

To fix this, common troubleshooting steps include turning airplane mode on and off, restarting the phone, checking and reseating the SIM card, updating carrier settings and iOS, moving to an area with better coverage, resetting network settings, and contacting your carrier for network outages or account issues. If hardware damage is suspected, professional repair might be necessary.