I'm going to piggy back off of your comment to say that I have no problems working "in the zone" in an open office. I can just ignore what is going around me. And I had HR sitting right behind me (as in 1.5m away) for a while. The sales guys were also quite close. Lots of loud phone calls.

Just to bring a counterweight to the usual "I'm a virtuoso that needs absolute silence to work" stuff that gets posted every time open offices get mentioned.