When Should You Hook Your Kid Up With A Cell Phone?

I was running some errands this weekend and I stumbled upon an interesting scene.

This little kid was running around the toy aisles, he must have been about 6 or 7 years old.  He had to have been on a sugar high to have that much energy.  Anyway, his mom was getting pretty upset with him and she told him to give her his cell phone.  Yes, you read that correctly...his cell phone.

At first, I wondered what a kid that young was doing with a cell phone and maybe there is some sort of special circumstance where his parents have allowed him to have one at such a young age.  Totally understandable but as a general rule, I think kids should be at least 13 before they get a cell phone.  They start participating in after school activities and they need to be able to get a hold of someone in an emergency.

What do you think -- at what age should parents get their children a cell phone?