iPhone OS 4 is arriving sometime this summer!  The major new iPhone OS features and improvements are:

• Multitasking (only available with iPhone 3GS and third-generation iPod touch 32GB and 64GB models from late 2009)
• Folders – organize your apps
• iBooks – read books on your iPhone
• Enhanced Mail – unified inbox, switch between inboxes more quickly, organize messages by threads, and the ability to open attachments in third-party apps

Other exciting new features and improvements include:

• Spell check
• Bluetooth keyboard support
• User-defined wallpaper
• Tap to focus when recording video and a 5x digital zoom for the camera
• Playlist creation and nested playlists
• Game Center — an official social gaming network for the iPhone

You can catch the official Apple keynote on the new iPhone OS 4 here.