[CurlyDave]

...plus the metal plane acts as a Faraday cage blocking almost all cell signal....

Not true.

The very simple observation is that my cell phone works just fine inside when the plane is sitting on the ground. Cell phone signals have a wavelength a less than 10 inches, they go right through the windows in the plane.

[Future Useless Eater]

Try it at ten miles up when the cell towers are below, not sideways to the plane.

I’m sitting on a plane now. Taking off soon. Will confirm tonight it likely gets zero bars above 30000 feet.