Actually, I'm surprised this doesn't happen more often:

Police in this Austin [Texas] suburb were stumped for hours by the 49 emergency calls that kept coming in from an unregistered cell phone. The caller would say nothing before hanging up, sometimes after a brief giggle. Eventually, though, police found their man, er child: a 7-year-old calling from his elementary school classroom just for kicks.

Having the cops show up to your first grade class must do amazing things for your concentration. Not to mention your underpants.