This is ancient, dating back to when cell phones didn't use encryption. As opposed to today, when many of them still use fundamentally broken encryption like A5/1 and A5/2, other than the ones doing something vaguely sensible like VoLTE. (Though I haven't heard anything about the ban on such devices being lifted.)

But in general, "you can't listen to this frequency" is completely crazy; "listen all you like but you won't get anything useful" makes more sense (along with "don't broadcast on this frequency above this power without a license").