Alone, the browser and search may not be enough. Facebook would still be dependent on users to choose its browser or search engine, or for other mobile platforms to employ them as the default browser or search--which is highly unlikely. But, if Facebook combines all three--browser, search, and smartphone--it may have a winner.
Without a Facebook-centric browser and search function, though, there would be little--if any--benefit from a Facebook smartphone. It would still rely on a third-party browser and search and wouldn't really generate any more revenue.
The smartphone business is tough, but it's not impossible. When the iPhone debuted, Apple's rivals didn't take it seriously. A few years ago there was no Android, and now it is the dominant smartphone platform.
If the rumors are true we'll have to wait and see if a Facebook smartphone platform can become the next iOS or Android, or if it ends up struggling like Windows Phone, or fizzling into obscurity like webOS.
Sign up for MIS Asia eNewsletters.