I have a gadget that I use in classrooms at the school I teach in Thailand. It's a simple device that nullifies mobile phone signals within a 50-60 foot radius. They can be purchased quite inexpensively on the Internet. Mine works off the mains but you can buy battery operated versions and some of them are even disguised as mobile phones so no-one will know its you that has created peace and quiet in the cabin.
Might I suggest that all seasoned travellers buy one now before demand grows and prices start increasing.
The alternative of course is to ask a cabin attendant for a glass of water then snatch the offending mobile from the moron using it and drop it into the glass - job done
