Apple has announced that iOS 4.2 is now available as a free download for iPhone, iPod touch and iPad. While iPhone and iPod touch users have enjoyed many of the features found in the latest version in iOS 4.0 and 4.1, it brings multitasking, fast app switching, folders, Game Center and a unified mail inbox to the iPad for the first time. The update also adds AirPrint and AirPlay to all compatible devices.

AirPlay allows users to stream music, video and photos wirelessly from iPad, iPhone and iPod touch to Apple TV, or to any stereo or powered speakers using AirPort Express. AirPlay-enabled speakers that allow content to be streamed directly to them are also set to hit the market over the next few months.

AirPrint lets users print directly from iOS devices to a number of HP ePrint printers on a local wireless network. HP PhotoSmart, HP LaserJet Pro and HP Officejet printers will be the first to support direct printing from an iOS device. Apple had previously said that users would be able to send print jobs to any printer as long as it is connected through a Mac or a PC, but that capability doesn’t look to have made it to the release version.

The update also makes the Find My iPhone feature, which was previously only available to MobileMe subscribers, free for all users. The Find My iPhone app, which is available as a free download from the App Store, lets users locate a missing device on a map and have it display a message and a sound. They can also remotely lock or wipe data from a lost device.

Aside from the iOS 4.0 and 4.1 features making their way to the iPad for the first time, the update also changes the functionality of the orientation-lock button. In a move that Apple says is to provide consistency with the iPhone and iPod touch, the button now acts as a mute switch.

The iOS 4.2 update is compatible with the iPhone 3G, 3GS and 4, the iPod touch 2G, 3G and 4G and the iPad. It is available now from Apple.