As you may already be aware, Hearthstone finally made its Android debut yesterday. If you attempted to play the game on an Android phone you would have quickly found out that the game has been designed and optimised for screens 6-inches and above, meaning you can't play on anything other than a tablet and a handful of truly massive android phones. Until now.
Android users being Android users, certain groups of people immediately set about trying create workarounds to this limitation, trying to find ways to bypass the 6-inch block. This reddit thread is dedicated to those efforts.
And it looks as though people have successfully managed to get the game running on their phones, but it is a firnickity process. This link provides a decent set of instructions, as does the above video. The solution is basically of side-loading using APK files. It's not piracy, especially when you consider that Hearthstone is free-to-play, but it is worth noting that Blizzard did optimise Hearthstone for tablets and ridiculously large phones. Bear that in mind before you embark on this journey.
That being said, this is Android and most likely you are an Android user because you like flexibility, open platforms and doing whatever the hell you like with your mobile devices. Most likely you'll be damned if you let Blizzard tell you what size screen is required for Hearthstone.