Highway call boxes

Not sure if this is the correct thread so feel free to move it if necessary.

If you have traveled on the highway/interstate, at least in the States, you notice call boxes at the mile markers. I was wondering how they worked. Do you just pick it up and it connects you with emergency services or is it an actual phone and you have to know the number to dial. I have never used one and it didn't seem like a good idea just to try one to see how it worked.

It's going to be the focus of a short story I'm writing so it's important to know how one works. The person who is going to use it will be 6-8 years old so I'm hoping it kinda just connects you to emergency services.

Thanks in advance.

cool that's exactly what I was hoping for considering the age of the caller and the fact that he's the only one who can get out of the car to use it due to a car crash to use the phone.

Thanks for the link RT. I have the idea of the call box working in a construction zone and it's not supposed too. That's what the signs say anyways.

Call boxes do not work in construction zones.

The four hour drive from Bradenton to Boca Raton really gives you time to think.

It's a short story set in Florida. But yeah I'll definitely a good thing to keep in mind when writing stories about anything.