promises over 100 new features including multitasking, folders, iBooks, improved Mail, spell checker, wireless keyboard support and the ability to change home screen wallpaper.

Apple notes: "iOS 4 works with iPhone 4, iPhone 3GS, and iPhone 3G. Not all features are compatible with all devices. For example, multitasking is available only with iPhone 4 and iPhone 3GS." The update is also compatible with the third generation iPod touch. A limited number of features also work with the second generation iPod touch. Unlike the previous 3.0 update, iPod touch users will not have to pay for the iOS 4 update. iPad users will have to wait until September for a compatible iOS 4 update.

1) Make sure you are using the latest version of iTunes. Connect your iPhone to your computer.2) When iTunes opens, select your iPhone under Devices in the Source List on the left.3) In the iPhone Summary pane, click Check for Update.4) Click Download and Install. Do not disconnect your iPhone until the update has finished.

The update comes a few days before Apple introduces the iPhone 4 on Thursday 24 June in UK, US, France, Germany and Japan.