Eh. You will burn down the phone battery in no time with that.
I prefer quiet phones. I acutally have the motor, sounds and everything turned off. It does not possess enough power to make a adquate music unless I added third party amps to the sound output jack. Im actually fearful that if I found a phone strong enough and have the right stuff boosting the music to where i can hear it... it will just combust spontaneously. We have always had that trouble since the cassette Sony Walkman days. That was like 40 years ago.
If you want a App that will make you a billionare, find a way to convert spoken speech that the phone can hear into text in real time. And if possible reverse the process and have a deafie type into it while it speaks a language that can be understood by whomever is present.
It may have been invented already, but I am not much of a smart phone person. My relationship with the darn thing is understanding just how crappy and cheap it really is and what I would need to do to find a replacement phone that absolutely rocks without destroying the bank. A friend of mine bought a fancy phone that was unlocked this year earlier. Put a insurance on it so that they fix break. Well it broke. And told us its 125 dollar deductable.
Threw that phone away for scrap and bought a samsung at 80 dollars outright and then tempered glass and armor covering for it. So you can drop it all the time and never break for about 125. Much better than some 300 dollar overcooked fragile crap that broke. What a loss.