"Gone Girl (...) unearths the secrets at the heart of a modern marriage. On the occasion of his fifth wedding anniversary, Nick Dunne (Ben Affleck) reports that his beautiful wife, Amy (Rosamund Pike), has gone missing. Under pressure from the police and a growing media frenzy, Nick’s portrait of a blissful union begins to crumble. Soon his lies, deceits and strange behavior have everyone asking the same dark question: Did Nick Dunne kill his wife?"
Thank you, Simon, for dropping all these promotional links. The official site for the film is findamazingamy.com, which clues you to further related social media outlets such as the film's Facebook and Twitter.
I haven't verified this myself but absolutely do take fanatic contributor Torrence's word for it: If you dial the number advertised on the billboard in the trailer, you get to hear an excerpt from the "Gone Girl" audiobook. Great find, thanks for letting us know!