T-Mobile customers across the U.S. said they couldn’t make calls or send text messages following an outage.

We tested with a T-Mobile phone in the office. Both calls to and from the T-Mobile phone failed. When we tried to send a text message, it said the message could not be sent. Access to mobile data appeared to be unaffected.

The outage began around 6pm ET.

Users took to social media to complain about the outage. Users across the U.S. said they were affected. A T-Mobile support account said the cell giant “engaged our engineers and are working on a resolution.”

In a tweet two hours into the outage, chief executive John Legere acknowledged the company was struggling to get back online but noted that the company had “already started to see signs of recovery.”

By 10:34pm ET, the issue had been resolved, tweeted T-Mobile chief technology officer Neville Ray, without saying what caused the four-hour long outage.

T-Mobile is the third largest cell carrier after Verizon (which owns TechCrunch) and AT&T. The company had its proposed $26.5 billion merger with Sprint approved by the Federal Communications Commission, despite a stream of state attorneys general lining up to block the deal.

Updated with acknowledgement by chief executive John Legere, and later from Neville Ray.