Carrier Verizon claims to have restored service across the country, but iPhone and Android users are still waiting to be told what happened — and how it can be prevented from happening again.

An SOS symbol appeared on the screens of iPhone users who use Verizon, where cell service bars are normally shown. According to Apple support, if you're having trouble with phone service and see SOS or "SOS only" in the status bar, your device can still make emergency calls despite not being connected to a phone network.