If mobile phones really are a safety threat to aircraft (as airlines and many here claim) then allowing them on planes in the first place is quite irresponsible. If they really are dangerous take them off passengers (and crew) at the security check, switch them off and hand them back at the other end.
Of course this would add significant time to loading/unloading, but safety is the first priority isn't it? On the other hand, if profitability is the first priority then carry on.