I actually got to hear the landline on a tour of ZFW.
The tour itself was pretty informative. It was two hours - an hour of ground and an hour in the center controller workstations.
ZFW Pilot Outreach to sign up for a tour.
I was more interested in what CPDLC looked like from the controller point of view. I rarely ever talk to ATC and just text them…
It was very neat seeing the aircraft send a CPDLC request, it shows up as a symbol on the aircraft tag. The controller does some tic-tacking on the keyboard and the symbol changes on the aircraft tag showing the uplink, the symbol changes again when the aircraft accepts or unables the uplink.
All while other aircraft are checking in and he’s ack-ing the aircraft check on.