Can you call a cell phone in the microwave?

Very nice, and I think you got to one of the issues at the very end.  the space between The grid matters. We are not dealing with inductive electric currents, we are dealing with electromagnetic radiation. The ratio of the grid openings and the frequency of the microwave radiation matters. Certain fractions of the frequency will block, and other fractions will allow passage. So you can have frequencies very close to the blocked frequency getting through.