I failed. This is extremely difficult. My iPhone 4 is stuck making a "bong" and vibration noise now when connected to a wall outlet or computer. I do not know what this means but based on my reading it has something to do with the power flex cable. I don't know how I broke it; I used gloves and didn't yank on anything. I think the cables are extremely fragile and are easily broken especially if they're old.
I would not recommend doing this (provided you aren't a professional) unless it's a spare phone that you're trying to fix for fun.