They should come up with a phone booth area on the plane, acoustically insulated from the rest.
I know, almost impossible given the premium per square inch on an airplane (and the trend of turning planes into little more than flying people-herding buses), but until there is something similar to that, this phone conversation idea on a plane is just plain ridiculous. Why allow something like that, when it's common policy (and common sense) to put your phone on mute in any public enclosed space (theaters, concert halls, restaurants, etc)?