Verge Network is running some "frequently asked questions" about missional. The first one is by Neil Cole, addressing: "What is a missional community?" There is a one-page printable pdf located on the link.
One thing it got me to thinking about was that perhaps there could be missional communities WITHIN a church organization. Like, they are not necessarily one-in-the-same thing, nor are they necessarily mutually exclusive. Still pondering that thought. It's worth a look-see though.