Can't help really, I've only ever had to call a vet out once in my life and it was because of a foster horse (that little pig) had gotten into more food than he could handle and colicked and I was unable to walk him through it.
To be honest, I've just never run into a situation where I needed a vet. I learned how to do my own shots a few years ago from my Grandma (she's been doing it for years), and in all honesty I just have the most health-amazing horse on the planet. I take care of any cuts she gets, watch for infections and fight it as they come... the only time I've come close to calling a vet was when she had a blown abscess- but it was already done in a few days. My family is very do-it ourselves sort of people.
However, I still have a number of a vet the next town over (the only one I know who does horses) in the case something goes seriously bad, and I keep my horse neighbor (who lives ten minutes away) on call as well, she has MANY years of experience that I have admittedly relied on more than once.
Really I think it's just as important to have people nearby who have experience and can help just as important as it is to know of a vet you can call when things go down the drain. Minor things though, like mud fever, small abscesses, colds, topical fungal infections, cuts and abrasions ect- I say just try to have a mentor and learn to do it yourself.
Hope that helps at least a little bit, if nothing else it's just some two-cents to add to the pile :)