Tess Coward, a 27-year-old PR professional based in New York City, woke up feeling under the weather on Wednesday. But without the ability to make phone calls or receive text messages, she couldn’t get in touch with her doctor or log into the provider’s patient portal.

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.

Verizon's services are fully back up. The carrier giant suggests restarting your device to reconnect it to the network. Additionally, the carrier is also giving all impacted Verizon users a $20 account credit to make up for the outage.

Verizon Communications has received the final approvals needed to buy fiber-optic broadband provider Frontier Communications after agreeing to some concessions to California regulators, including a small-business spending commitment.

Experts have told USA TODAY such outages can be dangerous and will continue. Verizon apologized to its customers and said it would be offering credits to everyone who was impacted. A spokesperson told USA TODAY that the outage was tied to a software issue and that the company is "conducting a full review of what happened.

Millions of Verizon Wireless customers across the country were hit with a massive service outage on Wednesday that left many wireless customers unable to call, text, or access the Internet for much of the day.