IMO it sounds about the same, which is decent b/c the HP out for the 3GS was pretty nice. Very little hiss, same soundstage, no radio-interference so far. My complaint is that even on the lowest setting, the volume is still too loud for "studying." With that said, that's just a preference b/c i like just soft ambient background music when studying. With my amp, I have excellent control of the volume through my IEMs.
Some posters complained the volume jumps too much for their preference, well it's still there. So if that annoys you, I figure you could do without an upgrade.
EDIT: Ok there is some interference that can be fixed on airplane mode, but you can't realistically expect no radio-interference from the phone.
Edited by spideyman409 - 6/30/10 at 4:48pm