I am making my phone in Blender and my mesh has weird artifacts on rounded corners only on render, not in viewport. Removing doubles and flipping normals doesn't help. I thought it's releated to non-quads on rounded surface but connecting verticles with knife tool also doesn't help.
You need to subdivide it into more faces. Here's what you get when you delete that n-gon and do grid fill:
The curvature is better but far from ideal (plus you get terrible topology).
Try to create a curve that has the same number of vertices for both sides (and try to keep the rest of the topology as quads)
I got it to look "right" without much work by triangulating those trouble faces, smooth-shading the object, and setting up auto-smooth.
Here is what the topology and render look like (click on it to view it full size in your browser...it's plenty high res):
And here is the blend: