Facebook is rumored to create a mobile phone. It just does not make sense that such a media company would invest so much time, and resources in building hardware or even in licensing existing hardware to build a phone.
Facebook has a 2 critical problems to solve on mobile. 2 only: app performance, app monetization. The first one being massive.
Facebook already has the critical mobile reach. This is already the most downloaded free iPhone app ever. But clearly not the most appreciated. They have massive reach of DAU/MAU (daily recurring users for simple humans)