The long awaited iOS 4 update for iPhone 3GS and iPod touch 3rd generation is available on iTunes now. It will also work with iPhone 3G and the 2nd gen touch, but some features may not function correctly.

Being the backbone of the new iPhone 4 (out on Thursday 24 June) the new operating software offers, among a few fixes, around 100 new features or changes, including the following:

Multitasking - Switch between apps (as long as they've been updated by the developer).

Folders - Put different apps into designated folders to keep the screens tidy.

iBooks - Sign up to Apple's ereader via iPhone and Touch, not just iPad.

Spellcheck - Has been updated with new words and everything.

Rotate and resize photos - Does what it says on the tin.

You can get a full rundown of the new main features in our iOS 4 breakdown. And we also reveal the lesser known, hidden features.