The Walking Dead is finally caught up to the other versions. Episode 4 was released for iOS yesterday (and the iOS version of episode 3 was released on October 18th). The game can be purchased in a multipack or as a single episode inside of the application.
Episode 5 should also be coming out soon for PC, Mac, Xbox Live Arcade, and PlayStation Network. No concrete release date has been given for Episode 5: No Time Yet yet, other than that it will release in November.