I have a iPhone app of wallpapers. They are for the older screen. What's the impact on iPhone wallpaper designers for the new, longer size?

What happens if we start incorporating for the new size and left the other wallpapers in the app alone?

How will the newer size wallpaper fit in the older phones? Will they be cropped top and bottom, top only, or bottom only, or resized to fill the screen?

What new coding schemes should we incorporate to accommodate the different sizes, if any?