Verizon says a software problem caused the glitch and they are conducting a postmortem, but experts say outages are "a fact of life" these days.

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.

The carrier says the outage is over and has apologized to customers. Here’s the latest on the issue — with no clear cause yet.

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.

With widespread outrage over missed appointments, no GPS, and the inability to log in to work apps, many say a $20 credit is not enough to make up for the incident.