I covered a social trivia game a couple months ago named TriviaPad. That particular game provided a trivia experience on the iPad only. A new trivia game, Trivie, has recently been released that provides a social trivia experience on the iPhone (and is playable on the iPad). Players can play Trivie with their friends by challenging them over Facebook, by contact list, or by username.
The asynchronous system for multiplayer games has become the go-to method for playing games with friends. Like most of those games, Trivie gives players a push notification when their friend has completed their turn and it's then their turn to participate. Trivie is built to look and feel like a game show (reminding me slightly of my favorite game show-like trivia game, You Don't Know Jack).
The game has over 75,000 questions in over 60 categories. The game also users slot machine mechanics and wagering to add to that game show feel. Trivie may also have real-time multiplayer in the future; the MMO infrastructure has already been built to handle it.
Trivie is available now for $1.99.