Since the inception of the App Store, and specifically since the big-name studios started throwing their hats in to the ring, iPhone gamers have been clamoring for big name series on the iPhone. Capcom brought Street Fighter 4 [$9.99], Square Enix developed an entirely new iPhone RPG, Chaos Rings [$12.99] and Konami is releasing a Castlevania puzzle game, Castlevania Puzzle: Encore of the Night.
According to Konami, Encore of the Night is an "addicting puzzle-RPG" where players will play as Alucard, the son of Dracula also seen in the classic Castlevania title, Symphony of the Night. The only details we know right now is that the game will involve playing as or against characters from Symphony of the Night, and completing puzzles will provide weapons and spells to help along the way.
It's hard to say if Encore of the Night is going to be closer to Puzzle Quest [$4.99 / Free], or more battle oriented like Capcom's Super Puzzle Fighter games-- Or something else completely different. As for why they're releasing a spin-off puzzle RPG instead of any of the other games in the series, your guess is as good as ours.
Konami rarely announces games like this without having them ready for release very soon. Their last game to appear on the App Store, MLB Power Pros Touch 2010 [$7.99], was first announced hardly even a day before it appeared for download. So, Castlevania Puzzle: Encore of the Night really could be available any time now.