In New Zealand it is illegal to use cellphones only during IFR flight. VFR flight? - do whatever you like.
"No person may operate any cellphone or other portable electronic device that is designed to transmit electromagnetic energy, on any aircraft while that aircraft is operating under IFR." - Civil Aviation Rule 91.7
However, as far as I know most regional airliners carry a cellphone in the cockpit for emergency use, eg in the event of comms failure or (worse) total avionics failure. Many flight instructors, including myself, do the same. Phones are switched off in flight of course.
O8
