I thought removing the plastic antenna cover was difficult. It was child's play compared to removing the iPhone's back case panel.
To remove the panel, I held the knife blade vertically and inserted it lengthwise between the back panel's edge and the front panel. Very gently, and for about 30 minutes, I worked on the back panel. Finally, I was able to separate one side of the back panel from the front panel. I then continued working the knife around the panel until both sides were loose.
Note: This photo shows me using the knife to merely hold the back panel away from the front panel. I did not use the knife in this manner to pry open the panel as it might have damaged the iPhone's internal components.
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