There is nothing worse than hearing one side of phone conversations when I'm trying to concentrate; it's like having a power drill grinding into my temple.
It seems like a lot of management types love open-plan offices because of the opportunities for serendipitous communication. I understand that, and can see the value if you're a CEO and your job is to be on top of things.
But a programmer's job is to be on the bottom of things. Hearing about some change to some component through the office chatter is completely immaterial to me and my day unless I'm actually working on that specific piece of code at that moment. All "being on top of things" means is that I'm distracted from the stuff I need to focus on.