I fly about 50-70K miles in a given year. I never turn my phone fully off, I usually put it in "Airplane mode" after I'm out of the coverage area (to conserve

I fly about 50-70K miles in a given year. I never turn my phone fully off, I usually put it in "Airplane mode" after I'm out of the coverage area (to conserve the battery so it's not trying to hunt to unreachable towers). I usually find that the phone has lost a signal well before we've hit the 10,000 ft. altitude where electronic devices are "allowed". Roughly this seems to happen about 8-12 minutes into the flight. I would consider the first 1,500 feet of altitude to be a zone where appearance of cellphones would be considered "normal", so the window in which you're truly in the supposed problem zone is even smaller. I'm not sure that the evidence your phone connected to some random carriers is any evidence that phones in flight could be problematic for modern towers. RF systems are also very interesting... I'm not an RF engineer, but I know enough about it that the cell towers coverage pattern is not spherical with equal coverage in all directions. The antennas would be designed and placed to direct the signals mostly out and to lower elevations, not up. Again, this would limit the chances that phones zooming overheard are appearing to multiple towers simultaneously, or moving tower to tower faster than the billing and tracking systems could manage.