iPhone 4 Power & Sensor Cable Replacement
"Also be sure to transfer the proximity sensor shroud/filter adhered to the old power & sensor cable if your new one does not already come with one."
It took me a while to figure out what they were referring to. Almost threw it out since it was stuck to the old flex! It's the little rectangular plastic piece with a little loop at the top left. You can see it in the middle of the power flex displayed in the previous step's picture. It seems it keeps the proximity sensor in place. It would be helpful if it were circled.
iPhone 4 Front Facing Camera Replacement
I found it easier to remove the camera after removing the headphone jack. The right side of the retainer was refusing to come off.