How come cell phones within close distances that may or may not have the same frequency can operate but not a?

Question

cell phone (s) being used in an airplain,etc...?

Answer 1

Cell phones may not be operated in an airplane; not because the are physically able to operate; but, because they interfere with the operation of the airplace avionics.  Some of the avionics abord a commercial airliner operates on the same frequencies as the cell phone (or close to it).  Radar systems, radio systems, remote sensors, etc. operate at frequencies close to some cell phones.  Interference is bad for the operation of the plane.  You would not want interference to inadvertently cause a plane to crash.

As for cell phones on the ground that operate on similar frequencies... they are either just far enough apart in frequency to operate properly, or they use another system of collision detection with frequency hopping, or spread-spectrum frequency (whose explanation is beyond the scope of this answer).

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