There are lots of apps on the Play Store which promise to earn you free bitcoins but trust me, nearly all of them are scams. I’ve found one legit mining app which does what it says. It actually mines bitcoins on your Android Phone, It’s one of the android bitcoin miner apps that actually work.
Again, you know mining on Android with GPU isn’t profitable. You won’t make huge amount of money by mining on your poor phone.
So, the android bitcoin miner I was talking about is ARM MINER and it is availing on the play store for free.
By entering your mining pool details, you can give it a go.