AT&T said the problem affected people trying to call customers of different carriers, but 911 and other emergency calls were not affected.

Tom's Guide lists the best cheap cell phone plans under $40, covering plans of different sizes including those with unlimited data. But even a $40 monthly payment may be out of the reach of some people, who still need to stay connected.

The FCC looks into a telecoms outage where AT&T users were suddenly unable to make calls to carriers like Verizon on Tuesday. AT&T says it's since resolved the issue.

AT&T and Verizon customers found themselves unable to call contacts on other carriers for several hours on June 4. Based on people's reports on Downdetector, the issue started at around 11AM ET for both carriers and peaked at approximately 5PM ET.

AT&T said late on Tuesday that an issue that had prevented making some calls to other wireless carriers had been resolved. Earlier, AT&T, Verizon and T-Mobile said they were all experiencing issues with some calls between carriers.

AT&T said Tuesday that it had resolved a nationwide issue that temporarily affected some customers’ ability to complete calls with another cellphone carrier. The company didn’t elaborate but said it was working with Verizon to determine the cause of an interoperability problem,

AT&T says customers facing a "nationwide issue" impacting their ability to call non-AT&T users has been resolved.

AT&T and some Verizon cellular customers might find it impossible to call outside their service providers customers until the respective communications companies diagnose and fix the respective problems.