There's no one shot method where you'll instantly become fluent. You just need to practice it. The more you do it, the better you'll get. And don't take personally (or at least don't try to) because most people are not trying to be rude, they most likely are confused and don't know you have a stutter. I know how frustrating it can be (and still is sometimes).. in fact the other day I called a store and the guy thought I was drunk lol. Anyway keep doing what you're doing and you'll soon become comfortable in the situation of talking on the phone, even it means starting off by talking to someone you're close with, who knows you very well.. stutter and all.