Whilst I can see why a Facebook Phone looks really promising from FB's perspective, to me, buying a Facebook phone because I like using FB is akin to buying a Coca Cola branded and manufactured car because I like drinking soda/soft drink.
Let's remember that the car companies >are< partnering with / branding with companies like Harley Davidson, Eddie Bauer, Orvis, etc. (Jeep has a Call of Duty: Black Ops branded Wrangler coming out next year.)
A "Facebook"-branded phone isn't such a long-shot, especially since Facebook is attempting to be your email/messaging/contacts database/... provider as well.
Likely as not Facebook will take a cue from Amazon, and produce a Android-no-Google phone (no Google maps, no GMail app, no Marketplace, basically nothing that requires a google authentication event. These will all be replaced by FB services.)
I suppose when Coca-cola makes it compelling for consumers to buy their car (ie, making the beverage better while driving "compatible" car), they can advertise it.
However, even WinPhone7 with deep FB integration didn't seem to really catch on with users (or at least, that wasn't a standout feature that brought users in).
Perhaps FB will stop updating their iOS/Android apps just to make Buffy look better?
