Many AT&T users in Oklahoma were without service for several hours on Thursday because of a nationwide outage.| MORE | AT&T customers report massive outage; Verizon and T-Mobile also down for someCustomers were unable to place calls, text or access the internet. Most of AT&T's network had been restored by late Thursday morning, and officials told KOCO 5 that it was completely restored by the afternoon."We have restored wireless service to all our affected customers. We sincerely apologize to them. Keeping our customers connected remains our top priority, and we are taking steps to ensure our customers do not experience this again in the future," an AT&T spokesperson told KOCO 5 in a statement.Oklahoma Department of Emergency Management officials said they were aware of the outage and urged people to use landlines and not call 911 to test their phones. The Oklahoma Highway Patrol and other law enforcement agencies said they saw cases where people calling 911 experienced a delay or couldn't connect. The Federal Communications Commission confirmed that it was investigating the outage. The White House says federal agencies are in touch with AT&T about network outages, but that it doesn’t have all the answers yet on what exactly led to the interruptions.>> Download the KOCO 5 app Although Verizon and T-Mobile customers reported some network outages, too, they appeared far less widespread. T-Mobile and Verizon said their networks were unaffected by AT&T’s service outage and customers reporting outages may have been unable to reach customers who use AT&T.CNN contributed to this article.Top HeadlinesPolice release preliminary autopsy information on death of 16-year-old Owasso High School studentOU in process of making changes in wake of executive order issued by StittOklahomans convicted of helping in a murder could soon serve more jail timeChina plans to send San Diego Zoo more pandas this year, reigniting its panda diplomacy