The following four steps can be accomplished without a plastic opening tool. However, it's recommended to use a tool to best avoid breaking any clips along the perimeter of the rear case.
Insert a plastic opening tool or fingernail into the notch in the gap between the rear case and the rest of the phone, located at the top of the device.
Gently twist the opening tool to disconnect the clips securing the top of the rear case.
Wedge the flat edge of a plastic opening tool in between the the earpiece/buttons/ambient light sensor ribbon cable and run it down to loosen the adhesive securing the ribbon cable.
Brilliant Step-By-Step guide. My phone needed new digitizer as just a black screen was showing when turned on, must have happened from a drop. I bought the digitizer screen combo from ebay and used this guide to dress across the components. Worked first time! There are a couple of other spongy or supportive rubber pieces around certain components that were in the original phone so I transferred those also, I guess they are there just to ensure tight connections etc. Absolute lifesaver!