well, it started out to be 45,000.
What was the original source of that information?
What radar facility in that area had the capability of reading altitude with the transponder turned off?
Cell phones are not usable at high altitudes because they hit so many cell towers that they drive the system nuts.
It didn’t stay at 45,000. The data say it went down rapidly to much lower levels, where cell phones were usable. Jamming? Possible. But I think this gives too much credit to the brain power of one guy-—which is about the only scenario that even remotely seems to fit outside of random accident, which I don’t fully rule out.