In a move that will please iPhone developers everywhere, Apple introduced the much-anticipated multitasking ability during an event highlighting the features of the iPhone 4.0 operating system.

Multitasking refers to the ability for the iPhone to run multiple apps and services at the same time. For instance, until now users of the Pandora app couldn’t utilize other iPhone functions while streaming music from the service. Now they can. For music apps, this is perhaps the most significant new feature, as it will allow users to stream music in the background while doing other things with their phone, likely leading to far greater usage of the phones streaming capabilities.

Pandora founder Tim Westergren was on hand at the San Francisco event to demo the new feature, where he revealed that more than 20,000 new Pandora users are added daily via the iPhone version of the service. With this new feature added, expect to see updates from virtually every streaming music service with an iPhone app, as many have been waiting for the ability to stream audio in the background before introducing new versions of their services.

Among the other new features of the new OS:
- Bakground location: apps can now use location data in new ways, such as instructing an app to “wake up” when the device is in a certain area.
- App folders: users can store their apps in folders marked by the category from which they were purchased in the App Store, such as Music or Games.
- Game Center: a sort of social network for gaming that includes leaderboards, multiplayer invites, achievement lists. Coming later this year.
- Developers can access the iPhone’s calendar, photo library, messaging tools and full mapping functions when designing their apps.

Apple also introduced an advertising platform called iAd that’s built into the new operating system. The idea is that in addition to selling apps, iPhone developers can now make money by selling ads inside their apps, keeping 60% of the revenues. Apple will handle all the ad sales and inventory management activities. Apple bought mobile advertising company Quattro Wireless this past January.

Jobs said the average iPhone user spends 30 minutes a day using apps on their device, which he translated to the opportunity for 10 ads per device each day. His goal, he says, is to serve 1 billion ad impressions a day by the end of the year.

The updated operating system will be released this summer for the iPhone 3GS and the third-generation iPod Touch. Older models will see some upgrades, but not all features, such as multitasking. The new technology will be available for the iPad later in the fall.

During the presentation, Apple CEO Steve Jobs also released some updated statistics on both the iPhone and iPad:
- 450,000 iPads sold since Saturday’s launch.
- 3.5 million apps downloaded since the launch.
- 4.5 billion apps downloaded from App Store to date.
- 85 million iPhones/iPod Touches sold.