With over 50 million iPhones sold to date, and 85 million iPhones and iPod touches in the hands of consumers, Apple held an event in Cupertino, CA today, to preview its new operating system (OS) for the iPhone, iPod touch, and iPad - iPhone OS 4. A beta version of the software was also released to iPhone Developers, including over 1,500 new APIs.

“iPhone OS 4 is the fourth major release of the world’s most advanced mobile operating system,” said Steve Jobs, Apple’s CEO. “We’re delivering over 100 new features, including multitasking, folders, a unified inbox, deeper Enterprise support, and an iPhone version of our iBooks reader and online iBookstore.”

Taking the stage, Steve Jobs and others showed off some of the more than 100 new features of the OS, which include multitasking, Voice over IP (VoIP), local notifications, task completion and fast app switching, folders, enhanced mail, iBooks for iPhone OS 4, improved features for enterprise, Game Center, and more. One of the most anticipated features for the iPhone OS, multitasking, was shown with simplicity clearly in mind. Users merely need to double-click the home button to bring up a window that shows all of the apps that are currently running. Similar to a taskbar, you simply scroll through the list of open apps to move between them. Now users can run an app such as Pandora in the background, and keep their music playing while they switch to another app to work on something else. Each open app also remembers where you left off, so you can pick up again right from the point you were at before. Like copy/paste, multitasking looks like it will be a great new addition to the iPhone OS.

Another feature to take advantage of multitasking in the iPhone OS is Voice over IP (VoIP). Now when you use an app such as Skype, you can switch to another app, and you'll get a double status bar to show you the status of your Skype call. Additionally, when Skype isn't running in the foreground, you can still receive calls, and be notified when those calls come in. Background location services can also take advantage of the new features in iPhone OS 4, letting you listen to music, for example, while your GPS continues to give you directions in the background. Task completion and fast app switching also benefit, by letting processes, such as uploading, happen in the background, while apps can restart instantly, remembering where you left off when last used.

Multitasking wasn't the only new feature Apple had up its sleeve. Folders allows you to organize your apps by creating a single folder to hold them in. To use the feature, you simply hold your finger on one of the app icons until the icons on the screen start to jiggle, then you drag the icon onto another icon you want to group it with, and release it. A new folder is created instantly, giving you the option to name it however you wish. Now, instead of having several pages of app icons to scroll through, you can group like apps into single folders, such as Games, Business, News, or any other grouping you can think of. An added benefit of this new feature is that instead of only being able to see 180 apps on your phone, you'll now be able to view over 2,000.

Enhanced mail was also featured, with a unified inbox, the ability to have more than one Exchange account, fast inbox switching (in case you want to focus on one account), and the option to organize e-mails by thread. In addition, the new enhanced mail will also feature the ability to get an attachment and open it with apps from the App store.

iBooks will also be available for the iPhone, with wireless syncing of your books between platforms, and a free Winnie The Pooh book, just like on the iPad. New features for enterprise included better data protection, mobile device management, wireless app distribution, multiple Exchange accounts, Exchange Server 2010, and SSL VPN support.

Enhancing the iPhone OS's ability to handle gaming, Apple also unveiled Game Center. With over 50,000 games and entertainment titles currently in the App store, Game Center will be a social gaming network of sorts, with invites for friends, matchmaking, leaderboards, and achievements. It will available later this year, and add yet another layer to the gaming experience on the iPhone, iPod touch, and iPad.

iAds, an in app feature developers can add to their apps, was also announced, with ads that appear in apps now focusing on interactivity with the user. The new iAds will also not take a user out of the app they are using, but instead let them view video inside the app, play games, and more in what essentially is like the ad being an app on its own, but running inside of the app being used, rather than outside of it. When a user is done with the ad, they are right back in the app where they left off. Apple is going to sell and host the ads, which run on HTML5, and split revenues with developers 60/40, with 60 percent of revenues for the ads going to the developer.