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More than 70,000 AT&T cellular customers reported being unable to connect to service early Thursday morning. While early reports suggested multiple carriers, including Verizon and T-Mobile, seemed to be affected, that appears to be a knock-on effect of a major network going down.

Service monitoring site Downdetector was showing multiple post-paid and pre-paid carriers as having increased outage reports starting at around 4 am Eastern time. An Ars editor in Texas has seen “SOS” on their iPhone since 4:30 am Eastern time and has been unable to make Wi-Fi calls.

AT&T acknowledged the outage to CNBC, telling the network that it was “working urgently to restore service” to customers and that it recommended Wi-Fi calling until service could be restored. Verizon and T-Mobile told CNBC that they suspected their customers were reporting outages when they could not reach customers on AT&T or resellers that use AT&T networks.