The rollout of Hearthstone for Android has already begun, with the game currently available for free on Google Play for players in Australia, Canada, and New Zealand. Gamers in other regions still have a bit of time to wait, but Blizzard promises that Hearthstone for Android will be available worldwide in the coming days (including on the Amazon Appstore for Kindle Fire owners). Android players will get to enjoy all of the content the game features elsewhere, including Curse of Naxxramas and Goblins vs Gnomes. Anyone playing a match on Android will also get a free pack of classic cards -- so there's no reason to wait!
Unfortunately, not all Android tablets will be supported: you'll need a tablet with at least a 6" screen and 1GB of RAM that runs Android 4.0 or higher. Check out the system requirements for full details.