Looks like iPhone4 uses the Helvetica NeuiUI fonts (located inside HelveticaNeue.ttc) as the preferred system font. There are four fonts inside this container:
font00.ttf = Helvetica Neue
font01.ttf = Helvetica Neue Bold
font02.ttf = Helvetica NeueUI
font03.ttf = Helvetica NeueUI Bold
I have not had luck yet making a new HelveticaNeue.ttc container file. My springboard keeps restarting until I put back the original one.
yes I'm going to give iNoRotate a try.You might try iNoRotate. It lets you control the orientation of your stock apps separately. Pretty cool; I'm using it now.