Couldn't CPDLC logging-on be made automatically? In my mind such a system becomes much more useful, specifically as a side-channel for lost comms, if the pilots didn't need to do anything except maybe once at the start of the flight (entering a callsign/ID/authentication, whatever), and it then handles log-ons by itself. I realize this might be difficult for technical and legal reason, such as it not being easy from GPS position to determine where to log in....