[alicorn]

We have unofficial office rules that work just like that. We do not have a sea of 50 people in the same space however, instead we have sort of isolated spaces that contain about 15-20 people each. All phone calls, chats longer than a minute or two ('I need to whiteboard this with you') and such are always done in small dedicated phone / meeting rooms on the sides of the open space. There is an adjacent coffee and food eating space shared by 3 such shared spaces, so about 40 people. It works well enough, almost everyone is mindful of sticking to the rules, since it benefits everybody to keep it that way.