Final Fantasy 4 has already landed on what seems like every other platform that exists, so Square Enix finally decided it was high time to port it to the one device you already have on you all the time anyway. The game has released on the iOS App Store for $15.99, and is mostly a port of the DS remake.
Since it's rooted in the 2008 DS version, the iOS app includes fully voiced CG cutscenes and 3D graphics that have been prettied up a bit for the nicer Apple screens. It also features a remixed score and a Jukebox for listening to the music, a mapping feature that starts a dungeon blank and is filled in as you explore, and the "Augment System" that lets you assign special abilities to characters.
If you're already up to your neck in FF4 ports, you'll be pleased to know that Square is going to be bringing other classic Final Fantasy games soon enough. The trailer for this release (via Siliconera) calls this the start of the "Final Fantasy mobile revolution." That revolution will apparently include ports of Final Fantasy V "and more." What could the "more" mean? Your guess is as good as ours.