Tizz,
In my office I have a 24 hour emergency phone number and I, like Jerry, have gone in to my office on evenings, weekends and holidays to assist those who are having pain in their teeth and jaws. It is pretty much expected in my region.
When I am away and or not available to see patients I have other local dentists look after my emergency calls and return the favor for them.
I guess not every dentist feels they need to be available for their petients outside of their regular office hours.
All the best,
Mike