AT&T announced on Tuesday evening that the issue preventing calls to certain other wireless carriers has been resolved.
Previously, AT&T, Verizon, and T-Mobile all reported problems with some calls between their networks.
In a statement, AT&T said: "The interoperability issues between carriers have been resolved. We've worked with other carriers to find a solution and appreciate our customers' patience."
Some customers in multiple states reported being unable to complete calls, prompting an investigation by the Federal Communications Commission.
Earlier, Verizon stated in a release that its network was operating normally but some customers in the Northeast and Midwest faced issues when calling or texting users on other networks.
According to tracking site Downdetector.com, as of 5:46 PM Eastern Time, there were over 2,300 outage reports, with Brooklyn, Chicago, and Philadelphia being the most reported areas.
T-Mobile US stated, "We are not experiencing network outages. We have noted an increase in reports from other providers on Down Detector, so this could be challenges our customers are facing when connecting with users on other networks."
In February, the Federal Communications Commission and New York Attorney General Letitia James announced they were investigating the cause of that month's AT&T network outage and its handling. The outage lasted over ten hours and impacted more than 70,000 customers.
AT&T compensated its customers with a full day's service due to the outage.
