A widespread cellular outage swept across the United States on Thursday, leaving millions of AT&T customers unable to make calls, send texts, or access the internet. While AT&T reported that three-quarters of its network had been restored later in the day, disruptions persisted for some users as the company worked to fully resolve the issue.

Although Verizon and T-Mobile also saw some network outages, they were significantly less widespread compared to AT&T. Verizon and T-Mobile assured customers that their networks were unaffected by AT&T's service outage, attributing reported outages to difficulties reaching AT&T customers.

The outage, which began around 4 am ET, affected over 74,000 AT&T customers, highlighting the scale of the disruption. While AT&T acknowledged the widespread outage, the company did not provide a specific reason for the system failure but urged affected customers to utilize Wi-Fi calling until service was fully restored.

While the cause of the outage remains unclear, industry insiders suggest it may be related to the handoff process between cellular networks, known as 'peering'. Despite speculation, there is no evidence to suggest the outage resulted from a cyberattack or malicious activity.

The outage had significant repercussions, with AT&T's stock experiencing a more than 2 percent decline. Local governments also reported disruptions to essential services, including 911 call centers and fire alarms.

As the nation grapples with the aftermath of the outage, the US Cybersecurity and Infrastructure Security Agency has pledged to work closely with AT&T to understand the cause and mitigate the impacts. Additionally, the Federal Communications Commission is expected to launch an investigation into the incident, as carriers are required to report information related to network disruptions.