It's too bad Apple didn't use the curved screen option for their next iPhone. According to a court filing, Apple considered building a phone with shaped glass, but it never happened because it would have cost too much money.
Network World discovered this of former Apple designer Douglas Satzger in which he details a curvy phone. Satzger worked as a top level industrial designer in Apple from 1996 to 2008. He is now the VP of Industrial Design at Intel. The design and manufacture of the shaped glass was deemed to complicated and expensive to be feasible, hence it's just a concept till today.
The technology in shaping the glass, the cost relative to shaping the glass at the time, and some of the design features of this specific shape were not liked.