The most effective method for repairing a cracked Samsung Galaxy S III screen is to install a replacement screen. Using a plastic opening tool, pry open the back case. Remove the battery and the SIM card. Using a heat gun, warm the front of the phone to 170 to 180 degrees Fahrenheit to loosen the glue. Using the opening tool, separate the edges of the screen from the phone. Remove the screen, and carefully place the replacement onto the phone.
Removing the glass can be troublesome, but having a screen protector can help. Alternatively use a piece of packing tape to hold the cracked screen together during removal. Use tweezers to pick up any small pieces of glass that are left behind.
The small metal speaker grill at the top of the screen usually is not included with the replacement screen. Remove it from the original, and place it in the new screen.
Before installing the replacement screen, make sure to clean up the excess glue from around the borders of the phone. A microfiber cloth with some WD40 or window cleaning solution can help with this.
The menu and return buttons are attached to the screen. When removing the original screen, carefully detach these buttons from the screen. While installing the replacement, use small pieces of sticker tape to hold the buttons in place.