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I would advice AGAINST opening any iPhone 4 or 4s.
Mine was opened and broke. Everything worked except the front camera. It's not the camera, it's something with the main board after removing the screen.
Don't do it. It's not worth it and white gets dirty very easily and looks like crap when every little space is filled with your black crud from your hands.
Don't do it.
If you don't believe me Google "front facing camera not working after screen replacement iPhone 4". And you'll see. I had the same issue. There's no way to fix it.
The people that have the threads in google were making a black iPhone white. Just like you.
Me. It happened after a cell repair booth here in Bangkok replaced my home button.
Same issue. Everything works and when you flip to the front camera the shutter gets stuck. Nothing fixes it. Not a software issue.
I took it to another repair place and they tried another camera. No luck. Just like the guys online. There is no fix for this problem. Once it's screwed it's screwed.
Maybe a replacement main board would fix it, but who knows
Don't do it.
So maybe it happens to one out of 4 or out of 10, but if YOU happen to be the lucky one you will never forgive yourself.