Apple CEO Steve Jobs introduced iPhone OS 4.0 on Thursday with an announcement sure to make many iPhone and iPad users happy: The new version of the operating system will include multi-task support so users can run multiple third-party apps simultaneously.

According to Mr. Jobs, Apple’s multi-tasking support will be superior to what’s offered on other mobile devices, and will keep your iPhone from “bogging down.” “We weren’t the first one to this,” Mr. Jobs said, “but I think we’ll be the best.”

Several different multi-tasking APIs will be available for developers, for features such as background music and audio playback and streaming, receiving incoming messages from services such as Skype, and tracking locations with turn-by-turn navigation apps.

Users will also be able to disable Location Services on an app-by-app basis, and apps can be organized into folder groups, making it easier to sort and find apps instead of flipping through multiple screens. The folders feature apparently lets users pack over 2,000 apps onto their iPhone or iPod touch, and iTunes 9.2 and newer supports iPhone folder management, too.

Mail users will be happy to finally see a unified In Box where they can see messages from all of their email accounts at once. The iPhone OS version of Mail also supports fast in box switching and viewing message threads.

Another feature likely to make iPhone owners happy will be support for Bluetooth keyboards. So far, the only iPhone OS device that supports using Bluetooth keyboards is the iPad.

iPhone OS 4.0 will also support wireless application distribution, and Mobile Device Management, and offers improved data security, which looks to be a nod to the enterprise market.

The bad news for first generation iPhone and iPhone 3G owners is that at least some of the features in iPhone OS 4.0 won’t be available to them. Multitasking, for example, will require an iPhone 3GS or third generation iPod touch — which is a hardware limitation, according to Mr. Jobs.

iPhone OS 4.0 will be available this summer for the iPhone and iPod touch, and this fall for the iPad. The beta of iPhone OS 4.0 and the SDK for developing iPhone OS 4-compatible apps is available for developers now at the Apple Developer Web site.

[This article has been updated with additional information about iPhone OS 4.0]