Apple has just turned on the switch for iOS 5. The next-generation OS for the iPhone/iPod touch and iPad is available now via an iTunes download.

The new software is available for download immediately, and iTunes 10.5 is required in order to install the update. Owners of Apple’s iPhone 4 (GSM and CDMA), iPhone 3GS, iPad 2, iPad and third and fourth-generation iPod touch handhelds have access to the new build, while owners of earlier devices will not be able to install the update.

First announced in June, iOS 5 includes over 200 new features including Notification Center, an innovative way to easily view and manage notifications in one place without interruption and iMessage™, a new messaging service that lets you easily send text messages, photos and videos between all iOS 5 users. Other features include untethered iOS updates for the first time, complete iCloud integration and new Camera features (called Camera 2.0).

To download iOS 5 in iTunes, be sure that your iPhone/iPod touch or iPad is connected to your computer. Next, go iTunes – Check For Updates. From there, follow the prompts.

For Mac users, there is also a Mac OS X update.

For a rundown on all that is new in iOS 5, please visit our roundup page.