Apple unveiled iPhone OS 4 software at a special event at its Cupertino, California -- and released a beta version of the software to iPhone Developer Program members. And, yes, it will include multitasking. Sweet.

The iPhone OS 4 beta release includes an updated Software Development Kit (SDK) with over 1,500 new Application Programming Interfaces (APIs) and over 100 new features that will be available to iPhone and iPod touch users this summer, according to Apple. At today's event, Apple CEO Steve Jobs said new features include multitasking for third party apps; Folders to better organize and access apps; improved Mail with a unified inbox, fast inbox switching and threaded messages; enhanced Enterprise support with even better data protection, mobile device management, wireless app distribution and more; Apple’s new iAd mobile advertising platform; and iBooks, the ebook reader and online bookstore recently debuted on the iPad.

iPhone OS 4’s new multitasking offers users a way to move between apps, and provides developers seven new multitasking services to add multitasking features to their apps. These services include background audio, so apps like Pandora can play music in the background, and VoIP, so VoIP apps can receive a VoIP call even when the iPhone is asleep or the user is running other apps. iPhone OS 4 provides multitasking to third party apps while preserving battery life and foreground app performance, which has until now proved elusive on mobile devices.

Folders help users better organize and quickly access their apps, according to Jobs. Simply drag one app icon onto another, and a new folder is automatically created. The folder is automatically given a name based on the App Store category of that app, such as “Games,” which the user can rename. Using folders, users can now organize and access over 2,000 apps on their iPhone. Users can also create and manage iPhone folders on their Mac or PC using iTunes 9.2.

iPhone OS 4 will also sport a new Unified Inbox for email, allowing users to see messages from all their email accounts displayed together in a single inbox. By tapping, users can switch between inboxes to see messages from any single account. In addition, users can now thread their messages by conversation, as well as open email attachments with compatible apps from the App Store.  

The iPhone OS 4 beta release includes a developer preview of Game Center, which contains a set of APIs that allows developers to create apps with the ability to invite friends to play a game, start a multiplayer game through matchmaking and track achievements and compare high scores on a leader board. Apps created with GameKit APIs will work with Game Center, Apple’s new social gaming network available to iPhone and iPod touch users later this year.

Jobs said new enterprise features in iPhone OS 4 include improvements in security, scalability and compatibility. The new Mobile Device Management service can be integrated with third party servers to wirelessly configure, query and even wipe or lock managed iPhones, and iPhone OS 4 enables enterprises to securely host and wirelessly distribute their own in-house developed apps to employees.

The new Data Protection feature uses a user’s passcode as an encryption key to protect mail messages and attachments stored on the iPhone. iPhone OS 4 now provides the option to set a longer, more complex passcode, making iPhone and its data even more secure. iPhone OS 4 allows IT managers to set up multiple Exchange ActiveSync accounts, is compatible with Exchange Server 2010 and includes support for forthcoming SSL VPN applications from Juniper Networks and Cisco.

The iPhone OS 4 beta software and SDK are available immediately for iPhone Developer Program members at developer.apple.com. iPhone OS 4 will be available as a software update to iPhone and iPod touch users this summer. A version of iPhone OS 4 will be coming to the iPad this fall.