You probably need to make an appointment at a local Apple Store. If none's available, I'd suggest calling Apple Support. AT&T doesn't really any expertise in providing tech support for iPhones, and there are no customer service reps who actively man this forum.
Be sure you are using your fingertip to slide and not trying with your fingernail. If it still doesn't work then you need to make an appointment with your nearest Apple Genius bar. http://www.apple.com/retail/geniusbar/