Rudas
It all has to do with CNS:ATM. Basically it logs on via VHF, SATNAV and enables the aircraft to constantly report to the logged on ATCC. IT is either FANS (Future Air Nav Systems) 1 for Boeing or A for Airbus.
It reduces the need to speak on a radio and the flight is continiously monitored, byt the ATCC concerned.
It is also part of the CPDLC - controller pilot data link communication, during which many of the commands/inputs/ comms will be done electronically as opposed to radio.
Much better system.
The A340 300s and 600s of SAA are equipped with it, as are 1 or 2 of the B747-400s.
There was a link to more information via the FAA web site and also Air Services Australia.