A few official repair videos for the iPhone 4 provided to Apple Authorized Service Centers have leaked online thanks to Sonny Dickson (via Lian).
That could be called the official tutorial, check them out.
iPhone 4 Vibe Motor Replacement:
iPhone 4 Sim Tray Replacement:
iPhone 4 Camera Test:
iPhone 4 (CMDA) Barcode Scanning:
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