I have a fringe and have had it and straightened it, in some way or another, for over 30 years now. I just look dreadful without it, my face is too long. I straighten it because left to it's own devices it doesn't curl properly, it just has a couple of weird kinks in it. My hair is a 3a/3b mix with the looser curls at the front and I have no root curl at all, it only curls from about 3" down (hence the lack of curl to the fringe itself). My fringe is a side one, not straight across and I think I can just about get away with it though it does look separate sometimes which bugs me no end.
To be honest, if I didn't need a fringe I wouldn't have one and if it would curl properly I would leave it curly - keeping it straight is a pain but I've just got used to dealing with it.
3b in South Australia.