I have it 100% and it´s still ridiculously quiet! 😡 It´s really embarrassing to keep shouting to my friends all the time "What? Could you speak up!", especially in public places. And my friends are always telling my to get rid of the crappy iPhone because of this annoying problem. Rather huge problem, because it´s main function is a phone after all.
No there´s nothing wrong with my ears, I´ve got very good hearing. And no my iPhone 4 isn´t faulty, one of my friend´s iPhone 4 has the exact same quiet volume.