A curved screen improves privacy, since it's less readable from the wrong angle. One disadvantage I can think of is that you'll no longer be able to use it as a mirror, because it will change your looks.
Perhaps a screen with variable curvature would be better. For that you would need a slightly flexible screen. That would keep the advantages of the flat screen and add the curved screen ones.
I think smartphone technology is going to develop very much in the coming years. Speakers have come down in size lately and I expect that small size will be used inside smartphones soon. My iPhone and iPad already have reasonably good sound quality without anything attached, like earphones or external speakers. In a few years that's going to be a lot better.
I read recently that the average smartphone user picks up his smartphone about 150 times a day. That amounts to about ten times/hour. Don't know if it's really been researched properly, but it seems credible. Whatever truth in that, I'm in no doubt that the smartphone is the most popular invention in the last 20 years, or even longer. Its great popularity indicates it's going to develop strongly in the coming years.