By AppleInsider Staff

Published: 02:10 PM EST (11:10 AM PST)

Because the iPhone OS runs on devices other than phones -- including the iPod touch and iPad -- Apple announced on Monday that it has renamed its mobile operating system to iOS 4, coming for free June 21 for the iPhone 3GS, iPhone 3G and iPod touch.

iOS 4

Calling iOS 4 "the most advanced mobile operating system in the world," Apple co-founder Steve Jobs announced at the Worldwide Developers Conference keynote that Apple was renaming the software. He also reintroduced some of the features unveiled earlier this year, including multitasking.

In a change from the past, it will be a free update for eligible iPod touch users (iOS 4 is not available for the first-generation device) when the operating system arrives on June 21 -- three days before the launch of iPhone 4.

After asking attendees to turn off their laptops and portable Wi-Fi hotspots in order to get a working connection, Jobs demonstrated the ability of the iOS to run Pandora in the background to stream Internet radio.

Jobs also showed off the unified inbox in the phone's Mail application, as well as threaded messages.

The chief executive also put applications into automatically created folders, as had been revealed in the initial unveiling of the new operating system. Folders can be renamed, and they can also be placed in the dock.

iOS 4 also adds support for Microsoft Bing for search, although Google will remain the default option. Jobs touted that Bing uses HTML5 for its mobile search results.

This month, Apple expects to sell its 100 millionth iOS-based device. Jobs said that shows that there is a large market for developers to make a profit.

The golden master candidate of iOS 4 is available for developers beginning immediately.

iAds

Also a part of iOS 4 is iAds, Apple's mobile advertising network. Developers are paid through iTunes Connect, just like with applications, and can add the ads in an afternoon, Jobs said.

"iAd offers advertisers the emotion of TV with the interactivity of the web, and offers users a new way to explore ads without being hijacked out of their favorite apps," Jobs said. "iAds will reach millions of iPhone and iPod touch users—a highly desirable demographic for advertisers—and provide developers a new way to earn money so they can continue developing free and low cost applications."

Apple has been selling 8 weeks of ads and has major clients including Nissan, Citibank, Sears, AT&T, GE, Best Buy, Target, Disney and more. The demonstration also included a Nissan advertisement for an electric car.

"iAd will allow Citi to reach millions of people on their iPhone and iPod touch," said Lisa Caputo, executive vice president and CMO, Citigroup. "iAd gives us a remarkable level of creativity for creating ads to connect with our current and future customers in a more interactive style than ever before."

The iAd network will be turned on July 1, and advertisers have already committed $60 million for the second half of 2010, which give make Apple 48 percent of the mobile advertising market. It will require users to upgrade to iOS 4.

"iAd is going to revolutionize mobile advertising," said Rob Master, North American media director, Unilever. "With iAd, we’ve been able to create some of our most powerful and compelling ads ever. iAd is the perfect mobile format to reach and engage with our customers."