I may be able to help with the reasons for asking for flight mode with mobiles. Placing the mobile into flight mode disables the radio transmitter in the mobile, so people playing games (stored on the mobile) or reading texts or documents (again stored on mobile) or even composing emails is not impeded. (they won't be sent until landed and out of flight mode).
There is a slight chance of interference with aircraft systems, but this is mainly theoretical, but the main reason for requiring mobiles to be off or in flight mode relates to the terrestrial mobile network. Base stations are arranged into cells with a particular set of radio frequencies allocated to each cell. However as there are not an infinite set of frequencies available, the frequencies are reused a few cells away.
Communicating with a mobile on the ground means your mobile connects to the cell tower in the cell you are located in. If you are mobile and move into a different cell the frequency of your mobile changes seamlessly and you move to the next tower, (next cell).
This is effective because you are only in the range of one or two towers at a time, and if two, there are different radio frequencies on each and the change over is automatic to the strongest signal, any other towers are 'over the horizon'.
However from an aircraft other towers are not over the horizon, at the set of frequencies your mobile is using, and will be received by more than one tower that is equipped with that set of frequencies, because you are at altitude the signal strength will be similar, and unfortunately the radio magic employed to switch your mobile seamlessly from one cell to the next will become confused and there is a possibility of locking up the whole mobile network.
In some places in the world mobile communication from planes is permitted, but this uses a different system, with your mobile switching to specific set of frequencies in the plane which becomes its own cell and a link from the plane to the network completes the connection.
(hope this helps, sorry it was so long winded), I was formerly a Senior Technical Officer with Telecom (before it became telstra) with responsibility for the mobile network, amongst other things.