IPhone OS 4.0

Here's a list of the features you'll see in iPhone OS 4.0:

Multitasking
Spell check
Bluetooth keyboard support
App folders for sorting apps
User-defined wallpaper
Tap to focus camcorder
5x digital zoom
Playlist creation and nested playlists
Enhanced email: Merged inbox view
sink to more than one account.
Fast inbox switching
Threaded messaging and in-app attachment viewing.
iBooks, able to wirelessly sync between platforms
Even more remote device management
Game Center: like Xbox Live, with achievements, leader boards, and matchmaking
iAds: mobile advertising system that gives free apps a way to earn cash