Switching Off Cellphones in Flight - Is it necessary?

Every time you board a flight and the air-hostesses give you n number of instructions of what to do and what not to, one thing is permanent across all the flights. 'Switch off your cellphones during the time between take-off and landing'. I always wondered why did we have to do that. They told me it interferes with the operations of the pilot while we are airborne.

This video here has a completely different point of view -



What do you think people?