Some 911 centers in Virginia, North Carolina, Texas and California reported that the outages prevented people from making emergency calls from their cellphones. Customers were advised to use a landline for any calls, or find a cellphone that uses a different carrier.

AT&T said customers should try WiFi calls on their phones until regular cell service is restored. “We are working urgently to restore service to them,” AT&T spokesman Jim Greer said.

Verizon said its service was not interrupted. “Some customers experienced issues this morning when calling or texting with customers served by another carrier,” Verizon spokeswoman Mariana Schlock said in an email. “We are continuing to monitor the situation.”

T-Mobile also said its network did not suffer an outage. “Down Detector is likely reflecting challenges our customers were having attempting to connect to users on other networks,” T-Mobile said.

AT&T had not acknowledged the outages on its main social media accounts as of 8 a.m., but in a reply to one complaint, the company referred to maintenance work.

“I would like to thank you for your patience while our systems are undergoing planned maintenance/being optimized for performance,” AT&T Help said on the social media site X.

Jacob Saur, administrator of Arlington County Public Safety Communications and Emergency Management in Virginia, said the department stopped receiving 911 calls from AT&T users around 6:30 a.m. and started receiving calls again around 6:45 a.m. The department detected no outages from other carriers and was still able to receive emergency texts from AT&T users, he said.

After communicating with other emergency departments, the Arlington County agency determined it was an outage throughout the Washington metropolitan area, Saur said.

AT&T customer Chip Chace said his cellphone had no service at 8:20 a.m. He said his cell service was off when he woke up Thursday at 6:30 a.m., with his service bars reading “SOS.”

“It’s definitely frustrating,” said Chace, a teacher from Fork Union, Va. “My wife works in D.C. during the week, so not being able to use my phone to talk to her in the morning while I take our son to day care is not ideal.”

Chace, who spoke to The Washington Post via direct messages on X, said he hoped the problem would be resolved soon. “It’s concerning because you don’t realize how important your cellphone is until you can’t use it,” he said.

This is a developing story and will be updated.