Head over to the home improvement store and get the biggest magnet you can find. Rub it around on the hard drive in an eccentric pattern to scramble any magnetic fields. (Guess why you shouldn't put magnets on your computer.) Don't repeat your pattern and just wipe that puppy clean. Next, take a drill and drill a bunch of holes into the hard drive itself.
I'll bet your cell phone had the battery still in it. When I get rid of one, I give it to the Sheriffs office. A female deputy takes the phone, wipes the storage and gives it to battered women who have left an abusive relationship. Even if it doesn't have current service, it can still call 911.
Your old hard drive doesn't have an internal power source (like a battery). Once it's scrambled, drilled and such, smack itwith a hammer. Take the pieces and throw them away in different trash bags.