Customers of AT&T, the country’s largest wireless provider, reported widespread outages on Thursday.

Some AT&T customers saw SOS messages displayed in the status bar on their cellphones. The message indicates that the device is having trouble connecting to their cellular provider’s network.

That can be a big problem in an emergency. AT&T urged customers to connect to Wi-Fi to use their phones.

Wi-Fi calling is a built-in feature on most Android devices and iPhones and can be turned on under the phone’s settings.

AT&T said Thursday it is working to restore service to wireless customers after people across the U.S. reported problems with making cell phone calls. 

Customers of the telecommunications giant began reporting problems on Downdetector, which tracks internet outages, after 3 a.m. ET. There were nearly 75,000 reports of outages around 9:15 a.m.

Cricket Wireless, which is owned by AT&T, also experienced network issues, with about 13,000 outages reported on Downdetector as of 9 a.m.

Tens of thousands of AT&T customers have been reporting outages this morning for their home phone, internet and mobile phone services, according to Downdetector.

The outages started popping up just before 3:30 a.m. ET, according to a graph shown on the website that tracks outages. As of 11:15 a.m. ET, the number of reports has declined to nearly 59,000 after spiking at more than 74,000 just after 9 a.m. ET.