Think this is also true for anyone who works in an open plan office. Any number of halfalogues can be going on at any one time, tough to tune them all out without an mp3 player of some kind.
Don't the authors of the article mean your attentional resources are drained because you can only hear half of the conversation? I think in most open offices one can hear both ends of the conversation, or do you mean you can hear people talking on the phone?