Thousands of people woke up Thursday morning to the dreaded SOS or SOS only message displayed in the status bar on their phones.

A cellular outage is affecting AT&T, T-Mobile and Verizon users across the United States, according to outage tracking website Downdetector.com.

What's causing the issue is unknown, and carriers are still determining when full service will be restored.

AT&T released a statement this morning encouraging its users to switch to Wi-Fi calling until service is restored.

Here's what to know.

How to turn on Wi-Fi calling: Seeing SOS on your AT&T iPhone? Here's how to turn on WiFi calling

Did a solar flare cause the AT&T outage?

After tens of thousands found themselves without cell service Thursday, many began wondering what exactly happened? The exact cause of the outage is still unknown but theories are, of course, swarming social media. One of the more interesting ones is whether or not it was caused by solar flares.

NASA confirmed that the sun emitted two strong solar flares Wednesday and Thursday.

The first one peaked Wednesday at 6:07 p.m. EST, and the second peaked Thursday at 1:32 a.m. EST. NASA’s Solar Dynamics Observatory captured an image of the event.

But experts say these probably aren't the culprits behind the outage.

Florida outage map: How to check status of services

How to turn on Wi-Fi calling

Here's how you can turn on Wi-Fi calling on your iPhone:

• Navigate to settings

• Tap Phone

• Then tap Wi-Fi calling

You may need to enter or confirm your address for emergency services, according to Apple.

Once Wi-Fi calling is available, you will see "Wi-Fi" in the status bar while viewing the Control Center.

When cellular service is available, your iPhone uses it for emergency calls. If you turn on Wi-Fi Calling and cellular service isn't available, emergency calls might use Wi-Fi calling.

Your device's location may be used to aid response efforts when you place

Why is my iPhone showing SOS or SOS only?

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.”

When your phone goes into SOS mode, it can still make emergency calls. When you make an emergency call with your iPhone, it automatically calls the local emergency number and shares your location information with emergency services.

Additionally, you can add emergency contacts under your phone’s medical ID options in the settings. Adding an emergency contact will alert them to your location with a text message after an emergency call ends.

How to get your phone out of SOS mode

In many cases, if your phone is in SOS mode, external circumstances outside your control could be responsible. However, there are some troubleshooting steps you can take on your end:

• Make sure you’re in an area with cellular network coverage

• Turn your cellular data off and then on:

  • Go to settings

  • Toggle cellular or mobile data off and then back on

• If you’re traveling internationally, make sure your phone is set up for data roaming:

  • Go to settings

  • Tap cellular

  • Cellular data options

  • Toggle data roaming

• Try restarting your device

• Check your carrier settings for an update

  • Make sure your device is connected to Wi-Fi or a cellular network

  • Open settings and navigate to General > About. If an update is available, you’ll see it here

• Turn your cellular line off and back on

  • Open settings

  • Tap Cellular and see if your cellular line is turned on

  • Don’t see a cellular line in settings? Setup an eSim or reinsert your physical SIM card

• Reset your network settings

  • Open settings

  • Tap General > Transfer or Reset [Device] > Reset > Reset network settings

  • Note: This will reset your Wi-Fi networks and passwords, cellular settings, VPN and APN settings you used before

• Update your iPhone to the latest version of iOS

  • Plug your device into power and connect to Wi-Fi

  • Go to settings > General and then tap “Software Update”

  • Choose the update you want to install

• Contact your wireless carrier

  • If all else fails, reach out to your carrier to see if there are any outages in the area, ensure your account is in active and good standing and make sure your device isn’t being blocked from receiving cellular service

How SOS works on iPhones

Making an SOS call on an iPhone 8 or newer is an easy, two-step process:

• Press and hold the side button and one of the volume buttons (either work) until the Emergency SOS slider appears.

• Drag the Emergency Call slider to call emergency services.

If you continue to hold down the side and volume buttons but don’t make an SOS call, a countdown will begin, and an alert will sound. Releasing the buttons after the countdown will automatically call emergency services.

Making SOS calls on iPhone 7 or earlier is just as simple:

• Rapidly pressing the side or top button five times will bring up the Emergency Call slider.

• Drag the SOS slider to call emergency services.

How to end an accidental SOS call

You can easily cancel an SOS call you started by accident, even after the countdown begins. To do so on an iPhone 8 or later, release the side button and the volume button before the countdown ends. To stop an SOS call on an iPhone 7 or earlier, press the stop button and then tap “Stop Calling.”

If the call begins, don’t hang up. Simply wait until a responder answers and explain that you made the call by mistake. Otherwise, the dispatcher may send responders to your phone’s location.

How to add emergency contacts

Here’s how you can add emergency contacts to your iPhone:

• Open the Health app and tap on your profile picture

• Open Medical ID

• Tap edit, then scroll to emergency contacts

• Tap the add button

• Tap a contact and add their relationship

• Tap done to save your settings

How to remove emergency contacts

Here’s how to remove emergency contacts:

• Open the Health app and tap on your profile picture

• Open Medical ID

• Tap edit, then scroll to emergency contacts

• Tap the delete button next to a contact

• Tap done to save your settings

This article originally appeared on Pensacola News Journal: Why AT&T iPhones are showing SOS. Here's what it means