So it seems you don't have to buy the latest version of the Jobs 2000 in order to get in on the new iPhone action. On 21 June, the iPhone 4.0 OS - iOS 4 as it's known to its friends - hits the shelves and the biggest surprise of all is that it's completely free. All you need to do is switch on your i-device, connect it to the internet and you'll be prompted to update your software but more about those first few steps soon.

The issue, and source of some confusion, is that the update isn't quite going to do the same thing for all of the devices. So, if you'd like to know in advance whether you'll be multitasking on your 2nd generation iPod Touch or tapping to focus on your iPhone 3G, here's a quick run down of the main features and which of them work on your device. (If you're wondering why the original iPhone and iPod touch aren't mentioned, that's because Apple has ceased to support them with further software. No update for those two. As for the iPad, you'll have to wait until the Autumn.)

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If you're not sure what all the rows in the table represent, then check out our full run down of iOS 4 for a better idea. Briefly speaking though, you get full functionality with the iPhone 4 handset and, with no internal gyroscope, front facing camera or second microphone in the 3GS, it's of little surprise that the new software has no effect in these departments for this slightly older phone.

It's a similar situation for the iPod touch third generation that's missing the magnetometer as well and therefore has no apps that will support a compass. Between the three of these devices - the iPhone 4, iPhone 3GS and 3rd gen touch - they essentially make the inner circle of those that receive most support from iOS 4.

Where it starts to break down is with the iPhone 3G and the 2nd gen touch. With these two devices not packing so much under the hood, there's a few things that they won't be able to do. First, and most frustrating of all for the owners, is that there'll be no multitasking. Worse still, and where the platform begins to appear fragmented in the way that Android already is, some of the more graphics hungry 3D gaming apps aren't going to be available on them either. There's also the slight annoyance of not being able to lock you device in portrait mode for whenever you'd rather the accelerometer didn't kick in.

Of course, there's still every reason to upgrade your OS no matter which of these devices you use. We just wanted you to know before you get too disappointed when you can't IM on Skype at the same time as listening to Spotify. No one needs to do that though, right?