AT&T has been feeding data to the US government since its founding For well over a century! Remember "The President's Analyst"?
All the main PTTs including AT&T were more or less founded in "partnership" with their sponsoring government. In the case of the UK, British Telecommunications was formed from part of the state-owned Post Office, and was deeply embedded in sigint in WW II (at Bletchley and other places, and developed the early Colossus computer at the Post Office research center at Dollis Hill). So, they've always done whatever spying the government's told them to. The thing that's changed of course, is the economics of mass surveillance makes it easy to keep the call records and use them in data mining. Ironically, listening in on phone calls is actually far better regulated then the situation on the internet proper, the main threat there is the extent to which they will apply voice recognition technologies to the calls. At least nominally they need a particularised warrant to listen in on a call, whereas that doesn't apply for mass surveillance of internet content.
The name has changed but currently active after some temporary suspensions: https://www.wired.com/story/hemisphere-das-white-house-surveillance-trillions-us-call-records/
