What's an OS and why does this one start with 'i'?
An OS is an operating system i.e. the most important software inside your iPhone that lets you run everything else. And iOS is just Apple's way of doing things on the iPhone, iPod and iPad: how you interact with apps, photos and games. Its slick touchscreen, with multi-touch capability, revolutionised smartphone usability.
Tip: go for the highest number
Just like those pop-ups on your computer or laptop reminding you to update everything, your iPhone will act perkier if it's running the latest version of iOs. Updates might fix bug and reception problems, improve battery life or add new features. All you need to do is head to apple.com to download the latest iOS (4.3.3) for free.
The iOS releases for iPhone you need to know about
iOS 2.0 introduced the App Store, "push" email and viewing MS Office attachments
iOS 3.0 gave us picture messaging, "copy and paste", video recording and shake to shuffle in the iPod
iOS 4.0 added multi-tasking between apps, FaceTime video calling over WiFi, folders to categorise your ever-growing app collection and unified inboxes for your email
iOS 4.2 introduced AirPlay streaming of video, music and photos over WiFi, improved battery life and even let us try out wireless printing
iOS 4.3 gave us the Personal Hotspot feature for sharing WiFi, improved Safari browsing and allowed us to cancel apps whilst downloading