The next operating system for the iPhone—iOS 6—comes with a few new nifty features and updates. You'll see a couple of those new features in Apple's Game Center, the leaderboard hub where you can track your friends' progress in various iOS games.
But what's new is that now you can challenge your friends, too.
Unfortunately nothing is yet synced enough or streamlined to have challenges open up a game at the mode you need to play, or remind you what score you need to beat. In-game Game Center options also vary depending on the game you're playing. While you could browse most of the Game Center in Super Hexagon (granted, catered to that specific game), for instance, Canabalt's options are limited to signing in and out.
The two applications—Game Center and whichever game you're playing—still feel limited by a wall between them, but we'll hopefully see developers coding games with the new Game Center features in mind in the very near future.