We're here at Facebook's phone announcement, and they haven't yet announced anything, but CEO Mark Zuckerberg is on stage talking about phones and apps, and how people use their phones. Zuckerberg says that phones should be designed around people, and not the apps on the phones themselves, noting that Facebook wants to do that with smartphones today.
Zuckerberg is talking about turning Android phones into a more social platform, and he brings up the fact that with Android's openness, along with Facebook's connected platform, people are built around this kind of ecosystem, so it makes sense that Facebook is wanting to do something about this.
Since people spend their lives sharing information with one another, via Facebook in this case, Zuckerberg and company want to make it easier for users to do just that on Android devices. However, before you can do that though, you must make the phone about the user first, and not the apps themselves.
Since Facebook has over 1 billion users, the company not only wants to make a phone, but an entire ecosystem around that phone, and it seems like they can sell a lot of them, touting that average smartphone sales are anywhere from 10-20 million, but Facebook's 1 billion users could easily surpass that.