Capoodle is right. There is usually a thin slot. If you don't have a coin thin enough, try a flat head screwdriver to get the cover off. And you are not alone. I haven't washed my cell phone, yet, but have washed a thumb drive. Sigh. I hope you manage somehow to get this working or one that you can manage.
There is usually a tiny cut away that a thin coin can flip the back of the case open. At the pharmacy I signed a form to be able to get the lids that are not child proof and after my daughter sliced her hand the web between the thumb and forefinger (needed sutures) I found a gadget that opens them as long as you keep your hand below the can. Let us know what can help you and one of us cuties may have a solution.
http://www.sears.com/search=pull%...
I'm lucky that I rarely have anything from the pharmacy ,though at the moment have a blister pack of pills for an infected finger.Husband has a lot of pills but they also come in blister packs & if you can easily open any stubborn blisters with scissors