However it does not work when the cell phone moves at M.80.
If you're thinking Doppler/Doppler shift might cause problems then is it worth considering what happens to the shift when you are near the overhead of the cell phone tower?
I have evidence that it is definitely possible to receive "welcome to" text messages in the cruise at or above FL350 (remote part of the world, flying at more than M 0.80). No idea if a voice or text "out" would work and I'm not going to experiment.