Was it already mentioned Cambridge had one in the early 70s?
Mooncrest; there's mediator and there's Mediator. Mediator (aka Mediocre)was the ATS system used at LATCC whilst a 'mediator line' was/is a line on the Air Traffic Operational Telephone Network (ATOTN), a dial up system still in use today but often set up at ATC units as 'speed dials' so you think they're direct lines when they're not.