While there were also smaller outage report spikes for Sprint (which has merged with T-Mobile), AT&T, Verizon (Engadget’s parent company) and US Cellular, the issue seems to be only on T-Mobile’s side. Spokespeople for AT&T and Verizon told Engadget their networks are working just fine.
Update (5:49 PM ET): T-Mobile’s customer service account on Twitter confirmed the problem, calling it a “widespread routing issue” and recommending subscribers try third-party services like FaceTime or Signal in the meantime.
Update (6/16 12:25 AM ET): The outage is still unresolved, however T-Mobile CEO Mike Sievert has issued a statement saying “We are recovering from this now but it may still take several more hours before customer calling and texting is fully recovered...This is an IP traffic related issue that has created significant capacity issues in the network core throughout the day. Data services have been working throughout the day and customers have been using services like FaceTime, iMessage, Google Meet, Google Duo, Zoom, Skype and others to connect.”
The CEO confirmed the issue has been going on since shortly after noon ET, and with a national issue stretching more than twelve hours, it has attracted quite a bit of attention. That includes the eye of FCC chair Ajit Pai, who tweeted “The FCC is launching an investigation. We're demanding answers—and so are American consumers.”
Update (6/16 1:22 AM ET): According to T-Mobile president of technology Neville Ray, “Voice and text services are now restored.” Despite rumors of a “DDoS” targeting various internet companies or cities, a thread by Cloudflare CEO Matthew Prince provides a better look at the “far more boring” reality of what happened, and why companies like his can see that there’s no evidence of an attack bringing down cellular networks.