Official iOS 4 changelog from Apple

Here's an official changelog for recently released iOS 4 for iPhone and iPod Touch:

This update contains over 100 new features, including the following:

• Multitasking support for third-party apps*
– Multitasking user interface to quickly move between apps
– Support for audio apps to play in the background
– VoIP apps can receive and maintain calls in the background or when device is asleep
– Apps can monitor location and take action while running in the background
– Alerts and messages can be pushed to apps using push and local notifications
– Apps can complete tasks in the background
• Folders to better organize and access apps
• Home screen Wallpaper*
• Mail improvements
– Unified inbox to view emails from all accounts in one place
– Fast inbox switching to quickly switch between different email accounts
– Threaded messages to view multiple emails from the same conversation
– Attachments can be opened with compatible third-party apps
– Search results can now be filed or deleted
– Option to select size of photo attachments
– Messages in the Outbox can be edited or deleted

• Support for iBooks and iBookstore (available from the App Store)
• Photo and Camera improvements
– 5x digital zoom when taking a photo**
– Tap to focus during video recording**
– Ability to sync Faces from iPhoto
– Geo-tagged photos appear on a map in Photos
• Ability to create and edit playlists on device
• Calendar invitations can be sent and accepted wirelessly with supported CalDAV servers
• Support for MobileMe calendar sharing
• Suggestions and recent searches appear during a web search
• Searchable SMS/MMS messages**
• Spotlight search can be continued on web and Wikipedia
• Enhanced location privacy
– New Location Services icon in the status bar
– Indication of which apps have requested your location in the last 24 hours
– Location Services can be toggled on or off for individual apps
• Automatic spellcheck
• Support for Bluetooth keyboards*
• iPod out to navigate music, podcasts and audiobooks through an iPod interface with compatible cars
• Support for iTunes gifting of apps
• Wireless notes syncing with IMAP-based mail accounts
• Persistent WiFi connection to receive push notifications*
• New setting for turning on/off cellular data only**
• Option to display the character count while composing new SMS/MMS**
• Visual Voicemail messages can be kept locally even if they have been deleted from the server**
• Control to lock portrait orientation*
• Audio playback controls for iPod and third-party audio apps*
• New languages, dictionaries and keyboards
• Accessibility enhancements*
• Bluetooth improvements
• Better data protection using the device passcode as an encryption key* (Requires full restore.)
• Support for third-party Mobile Device Management solutions
• Enables wireless distribution of enterprise applications
• Exchange Server 2010 compatibility
• Support for multiple Exchange ActiveSync accounts
• Support for Juniper Junos Pulse and Cisco AnyConnect SSL VPN apps (available from the App Store)
• More than 1,500 new developer APIs
• Bug fixes

Products compatible with this software update:
• iPhone 3G
• iPhone 3GS
• iPhone 4
• iPod touch 2nd generation
• iPod touch 3rd generation (late 2009 models with 32GB or 64GB)

* Requires iPhone 3GS, iPhone 4, and iPod touch 3rd generation.
** Requires iPhone 3G, iPhone 3GS, and iPhone 4. SMS/MMS messaging and Visual Voicemail require support from your wireless carrier.

For feature descriptions and complete instructions, see the user guides for iPhone and iPod touch at:
http://support.apple.com/manuals/iphone
http://support.apple.com/manuals/ipodtouch

For more information about iPhone and iPod touch, go to:
http://www.apple.com/iphone
http://www.apple.com/ipodtouch

To troubleshoot your iPhone or iPod touch, or to view additional support information go to:
http://www.apple.com/support/iphone
http://www.apple.com/support/ipodtouch

For information on the security content of this update, please visit this website:
http://support.apple.com/kb/HT1222