A major telecommunications outage is unfolding, with a surge of error reports pointing to widespread service disruptions across Verizon, AT&T, and T-Mobile. In particular, many Verizon customers are reporting that their phones have gone into SOS mode, though they should still be able to make 911 calls via satellite.

Verizon said Thursday that it would begin issuing $20 credits to the accounts of customers affected by Wednesday’s nearly daylong cellular service problems.

Problem reports with Verizon wireless service began to spike just after noon ET, with more than 177,000 error reports submitted as of 12:48 p.m. on Tuesday, per uptime-monitoring site Downdetector.