What do you need to know about iPhone OS 4.0? Here you go:

Multitasking

• Pulls up a dock on the bottom of the screen when you double-click the home key. The dock displays all of your programs that are “running.”
• Programs aren’t really “running” in the background. Instead, Apple gives apps access to 7 actions to essentially multitask. These are: Background audio, VOIP, Background Location, Push notifications, Local notifications, Task completion and Fast app switching.
• Apps frozen still essentially, so when you boot them back up, it’ll return to normal state – great for games, I’d imagine.
• Background audio now allowed. Pandora runs in the background and can use iPod’s lock screen controls.
• VOIP good to go. You can leave on Skype and it acts just like a regular phone call, but with a red bar on the top when you navigate away from Skype.
• Task completion – finish uploading a photo to Flickr (per their example) but navigate away from the app
• Push notifications from apps – That Flickr reminder could in theory pop up if there’s a problem uploading a file.

Folders

• You can put apps in folders now to organize them. That way you can organize these folders with multiple items inside of them, giving you more room for more apps.
• Folders can be installed on the dock as well.
• The image of a folder contains smaller images of the apps inside.
• 2160 Total Apps available per phone

Wallpaper

• Background for all app screens, just like the iPad.
• Can be different for Lock screen and app screen

Mail

• Unified Inbox (thank god!)
• Multiple Exchange accounts allowed
• Follow threads by tapping on “>>” icon
• Fast inbox switching for going to a dedicated inbox if need be
• Open attachments with third party apps from the app store

iBooks

• Support for iPhone
• Wirelessly syncs books and bookmarks from iPad

Enterprise

• Mail encryption
• Wireless app distribution for local companies (You host the app on your server, distribute to clients)
• Exchange Server 2010
• SSL VPN Support

Game Center

• Social gaming network
• Invite friends, do matchmaking, leaderboards. Think XBox Live for the iPhone

iAd

• Mobile advertising for the iPhone OS
• A way to fund free apps, that is “better” than current models
• Jobs says that people spend 30 minutes in apps each day
• Apps are interactive and keep the user inside the app they’re currently in
• Apple hosts ads on their servers, does a 60/40 split (Developers get 60%)
• All coded in HTML5
• Tap the banner, and ad pulls up. Then click the “X” icon at the top left corner of the ad, and you’re back in the app
• Games, maps and videos can be in the ad, making it completely interactive
• In-ad purchasing as well

The Miscellaneous Stuff

• Bluetooth keyboards for iPhone
• Tap to focus for video
• Calendar access to developers
• In-app SMS (brilliant)
• Half-curl page transition – like in iBooks

Availability:

• iPhone 3GS and 3rd Gen iPod Touch get everything this summer
• iPhone 3G and 2nd Gen iPod Touch get some but not all features this summer (And they’re not including multitasking)
• iPad Fall 2010