Blizzard has just released a blog post about the development of hearthstone on mobile and its progress. As of now Blizzard has revealed that they do have a version of hearthstone up and running on Android and iPhone. However, they have said that have much more work to do, pushing back the release date until next year. The main culprit for this delay is dealing with the smaller sizes of phone screens.
One of the biggest challenges with that is revamping the user interface so it feels intuitive and offers the same quality _hearthstone experience, but this time from the palm of your hand.
On a good note for Android users, as for most applications on the platform, you can install tablet applications on phones. If you can handle playing with a small UI, you might get a chance to play hearthstone on-the-go before everyone else.