The U.S. Federal Communications Commission's report comes after a five-month investigation, which led the agency to refer the matter to its Enforcement Bureau for potential violations of FCC rules, which could result in a fine.
The FCC said all voice and 5G data services for AT&T wireless customers were unavailable during the outage affecting more than 125 million devices.
Voice and 5G data services were also unavailable to customers of other wireless providers that regularly use or were roaming on AT&T’s network and it cut off services to devices operated by public safety users of the First Responder Network Authority. The FCC said AT&T prioritized restoring services to first responders but did not notify those customers until three hours after it began and nearly an hour after it was restored.
The incident began after AT&T implemented a network change with an equipment configuration error, the FCC said, adding that network operators must adhere to their internal procedures and industry best practices when implementing network changes.
"We have implemented changes to prevent what happened in February from occurring again," AT&T said in a statement on Monday. "We fell short of the standards that we hold ourselves to, and we regret that we failed to meet the expectations of our customers and the public safety community."
The company in February said it would credit customers a full day of service for the carrier's outage, calling it the "right thing to do."
The FCC offered recommendations to help prevent similar outages in the future.
"This ‘sunny day’ outage prevented consumers across the country from communicating, including by blocking 911 calls," said FCC Chair Jessica Rosenworcel. "We take this incident seriously and are working to provide accountability for this lapse in service and prevent similar outages in the future."
The FCC is also investigating a massive hacking incident in April disclosed earlier this month that resulted in the illegal downloading of about 109 million AT&T customer accounts.
