You can play white noise on the headphones. It mutes other sounds without drawing attention to itself.
Conversely, if an office with a closed office plan has a culture where closed doors are common and it's rude to knock, then collaboration will definitely be hindered.
We need to collaborate and to work in peace and quiet. This is probably why it oscillates between open and closed office plans. Neither solution is perfect. The best solution is probably default closed offices with a culture of having your door open and lots of collaborating spaces that are actually used.
This is what I have right now at Microsoft and it's awesome. Everyone on my team has a private office, and we have plenty of collaboration spaces, including conference rooms as well as less formal gathering spaces between blocks of offices and near the food areas, plus a few large open areas dedicated for meetings (these are more isolated from offices, and generally used like conference rooms, but open to the hallways, with curtains that can be used to isolate a bit more).