This may come in handy someday if you have remote door unlock on your car.
Good reason to own a cell phone: If you lock your keys in the car and the spare keys are home, call someone on your cell phone. Hold your cell phone about a foot from your car door and have the other person at your home press the unlock button, holding it near the phone on their end. Your car will unlock. Saves someone from having to drive your keys to you. Distance is no object. You could be hundreds of miles away, and if you can reach someone who has the other "remote" for your car, you can unlock the doors (or the trunk).