Sadly that's the problem for most of the non-stutterers (I don't call them normal people because we all are normal!): they don't understand how it effects us. When I have to make a phone call I always try to use words I know I usually don't have a problem to say them but it's like my brain thinks "oh, she's using the phone, let's see about that". Like you said: it is frustrating and believe me, I feel helpless most of the time when it comes to this. I feel like there's sadly not a solution, because every stutter is different and every human being is unique in it's own way, there are only techniques and a "tool kit" that can help to make it easier. Sometimes when I get frustrated or sorry for myself because of my stutter I think about what people told me I couldn't do or achieve and I did it anyway. (Damn I know I'm not really helping, sorry!)