I don't know, to be honest - I do suspect the problem is much smaller now that 3/4G is a thing, though - higher data rates means smaller cells means more direct

I don't know, to be honest - I do suspect the problem is much smaller now that 3/4G is a thing, though - higher data rates means smaller cells means more directional antennas, and presumably carriers will not waste energy beaming skyward - so maybe airborne phones don't see as many cells as they used to (if any). It would be non-trivial to determine the phone's altitude, but you could make a pretty good inference from the number and location of cells reporting that they 'see' it - and the velocity should be a no-brainer to figure out with a reasonable degree of accuracy. Hm. Just a semi-educated guess. (I haven't looked at cellular systems since I was in university 15-20 years ago.) Methinks you are probably right.