T-Mobile, one of the three largest mobile carriers in the U.S., said it's working to fix a widespread network issue.
The scope of the outage wasn't clear, but Ray said it has affected customers around the country. T-Mobile representatives did not reply to further questions.
AT&T and Verizon both said their networks were operating normally. But calls between their customers and T-Mobile customers could have problems because of T-Mobile's issues.
T-Mobile became one of the country's largest carriers, along with AT&T and Verizon, after buying rival Sprint. The company has started integrating the two networks.
The Federal Communications Commission, which oversees voice and data networks, said its public-safety bureau is looking into the problem.
T-Mobile paid a $17.5 million fine for two nationwide service outages on the same day in August 2014, which together lasted three hours and prevented customers from being able to call 911.