That's the point, it's not binary between open plan or individual offices... you can have 2, 3 or 4 - people shared offices.

http://c2.com/cgi/wiki?PeoplewareOnSharedSpaces

"enclosed offices need not be one-person offices. The two- or three- or four-person office makes a lot more sense, particularly if office groupings can be made to align with work groups. Even in open-plan offices, co-workers should be encouraged to modify the grid to put their areas together into small suites. When this is allowed, people become positively ingenious in laying out the area to serve all their needs: work space, meeting space, and social space. Since they tend to be in interaction mode together or simultaneously in flow mode, they have less noise clash with each other than they would with randomly selected neighbors."