When iPhones aren’t connected to a cellular network, they will typically alert the user by giving an indication in the phone’s status bar. Those notifications usually say “No Service” or “Searching,” but your phone may also say “SOS” or “SOS only.”

In short, when you see SOS on your phone, it means you're not connected to a cellular network. "If you see SOS or 'SOS only' in the status bar, your device isn't connected to your cellular network, but you can still make emergency calls through other carrier networks," reads an Apple support page on the feature.

As of last night, Verizon has confirmed that the reported outage affecting millions of users has been resolved.