For those who haven't heard of it, Hearthstone from Blizzard is a virtual collectible card game set in the World of Warcraft universe. It uses turn-based mechanics and is similar to the real-world collectible card game Magic: The Gathering. The game has been available on Android tablets for some time now, but the latest news is that Blizzard was able to create a version for Android smartphones (and the iPhone) now too.

Here's a quick quote from Blizzard regarding the more mobile version of the game:

Never played Hearthstone? No problem! Just download the app and run through a few lighthearted tutorial missions to get a handle on the basics of this quick and fun collectible card game. Before you know it, you’ll be slinging cards as your favorite hero in Play Mode against friends and other players alike. Soon, you’ll be on your way to earning card packs, in-game gold, and arcane dust as you command a colorful cast of characters into the fray.

Already playing Hearthstone? Your card collection and progress are shared across any device that you use to play the game. That means all the cards you’ve collected will be waiting for you whenever you enjoy Hearthstone on your mobile phone.
Source: Hearthstone® Now Available on Mobile - News - Hearthstone