1. Remove the Otterbox outer rubber cover (fingernails along the rubber seams should do the trick)
2. Using a table knife (or any knife with a rounded tip), insert the tip of the knife at one of the rounded corners of the Otterbox case into the seam between the top and bottom plastic covers.
3. With the knife in the seam, gently angle the knife just enough to separate the top and bottom covers a bit. Now guide the table knife along the seam from the rounded corner to one of the plastic hinges. The hinge will pop open as the knife approaches it.
4. Repeat the same process at the other three rounded corners of the phone, so that a few more plastic hinges will be opened.
5. Now repeat the process from the sides of the phone, guiding the angled knife toward any unopened hinges.
6. Eventually you will have popped open all of the plastic hinges and may remove the top cover.