I looked up CPDLC quickly and the whole thing brought back memories of multiple meetings of FAA, ICAO, FANS groups etc. This datalink system was the hot topic back then, and ALL the airlines, FAA people insisted that voice should always be available no matter what/how data links were used. Good they have some sort of implementation. And it seems to be primarily Inmarsat data links- not surprised. They had been doing this with ships for a while, and had the most experience, and more important to the industry - most credibility.
Inmarsat wanted to implement a different modulation scheme (for satellite transmission) for the airline system, and as a contractor, I was charged with technically evaluating it. When talking to me about it, the FAA/ICAO guys (who were nontechnical people and primarily managers and administrators) would refer to it as the 'squiggles in the air'.... lol.