Another thought on this - I think I'm right to say that one of the reasons why people are asked not to use cell phones on planes is that altitude increases the number of cells a phone can reach - someone hovering a couple of miles above Metropolis might block one of the frequencies used in dozens of cells, not just the two or three a cellphone usually utilises. So if Clark ever uses his cell phone while flying he might get some awkward questions from the FCC...
