That's always been the rule.  They're much more stringent during takeoffs
and landings than while in routine flight.  It's only a guess, but I think
this is because the spacing of planes is much more critical at these times,
so there isn't as much time to ask for a retransmission of a radio contact
between ground and plane if one is garbled by on-board consumer electronic
gear.

BTW, as a matter of general information, the telephones that are used in
commercial aircraft (the ones you put your credit card in) aren't "standard"
cell phones, or so I've been told.  They use different frequencies and the
system has been specifically designed not to conflict with avionics.  The
statement that it's only a money issue simply isn't the case ... you're not
forbidden to use your cell phone merely because they want the money from use
of the installed system; the two systems aren't the same and the one has
been designed specifically for use in commercial aircraft.

--
 Walt Smith - Raleigh, NC
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