Outwardly, the new iPhone 4S shares the same design and build quality of the iPhone 4. They both have flat front and back glass panels with a metal band around the edge that functions as part of the antenna. That band caused some controversy with the iPhone 4, as many users lost signal when they held it, but we're told that issue has been resolved on the iPhone 4S.
The 3GS is somewhat fatter than the 4 and 4S and we don't think it sits as snugly in the hand. Its extra size won't be good if you make a habit of wearing super-skinny jeans.
The 4 and 4S are available in white, which is great news if you don't like all the drab dark phones on the market at the moment. The 3GS is only available in black on Apple's online store, but you can pick up a white version from various resellers online.
The iPhone 4 was the first of Apple's phones to use what it calls a retina display, which basically means it's supremely sharp. It makes reading even the tiniest of text on webpages perfectly comfortable. It also displays colours very well, so photos and videos both look awesome.
The iPhone 4S has exactly the same screen, which means you're still getting probably the best mobile phone display on offer at the moment -- although we were hoping for a larger screen as part of the iPhone 5.
Of course, such a high-quality screen comes at a price, so if super high definition and glorious colours aren't as much of a priority you can save yourself a few bob and plump for the 3GS -- it's still a good screen and does the job well for apps and such, you just shouldn't compare it side-by-side to the iPhone 4 or it may make you weep.
All three phones pack different processors capable of varying levels of power. The iPhone 3GS's processor was a pleasing step up from the 3G, but the iPhone 4 saw the inclusion of Apple's A4 chip bringing speedy performance and impressive graphical ability for running the 3D gaming apps such as Infinity Blade.
The iPhone 4S however is packing the new dual-core A5 chip Apple reckons will make its graphics seven times faster than the iPhone 4. If that's true, expect apps to load in super-quick time and demanding 3D games to run very smoothly. We'll have to wait until we spend some real time with the new phone to see if those claims stack up.
The iPhone 4S also promises data download speeds of up to 14.4Mbps, which is a decent improvement from the roughly 10Mbps offered on the iPhone 4 and a leap ahead of the 3GS's 7.2. The higher speeds offered on the iPhone 4S mean that Web browsing and downloading songs and videos should be much quicker -- good news for those of you wanting to use Apple's iTunes Match service.
These speeds are all very much dependent on our own UK networks as well as the phone's connectivity, so we'll have to wait and see how they measure up when we get our hands on for a full test.
One of the main upgrades of the iPhone 4S is the camera. It now uses an 8-megapixel sensor that's back-illuminated, which should make it much more capable in low-light situations. It can also shoot 1080p video.
The iPhone 4 packed a 5-megapixel camera that could shoot 720p video. We liked the 4's camera and love editing our pictures on the plethora of photography apps available on the App Store. But it was definitely starting to lag behind much of the smart phone competition who were flying ahead with full HD video.
The iPhone 3GS has only a 3-megapixel camera and no flash, so low-light photos are pretty much out of the question. If you'll be wanting to get some shots of your friends in a dingy bar, we suggest you go for the 4 or 4S, unless you plan on carrying around studio lights.
The iPhone 4S promises a much better camera experience, so if you're a massive shutterbug you should think about stretching your wallet. We're yet to give it a thorough test though, so make sure you check out our full review before you splash your cash.
The iPhone 4 and 4S both feature front-facing cameras so you can enjoy the delights of FaceTiming -- that's video calling -- other iPhone owners.
Which phone you eventually plump for will probably be determined in large part by the amount of money sat gathering dust in your bank. UK providers are yet to announce their price offerings for the iPhone 4S, but it will be available to buy SIM-free from £500, which is usually the cheapest way of doing it if you've the cash spare.
The iPhone 4 is now available in an 8GB version, which brings with it a lower price tag. You can buy it SIM-free from Apple for £430 or get one free on a contract of around £40 per month. These prices are likely to change when the iPhone 4S lands in stores, so keep your eyes peeled.
The iPhone 3GS is by far the cheapest offering, so if you don't need
the higher end features of speed, cameras and voice control you can
pick yourself up a bargain. It's available SIM-free from Apple
for £320 or free from most networks from around £15 per month.
Extras: Voice control, AirPlay
Voice control has been present on iPhones before, but has never really worked that well and pretty much only allowed you to say "Call Steve", which it never seemed to get right. Sorry about all those wrong calls, Dave.
The iPhone 4S brings a service called Siri that makes voice control a much more usable feature. Asking "do I need an umbrella today?" for example, will result in your phone automatically searching and displaying the latest weather results.
You can also use it to set reminders, read and reply to texts and numerous other tasks all without having to place finger to screen. From the demo we saw, we're very impressed and we're really looking forward to giving it a proper test.
The iOS 4 updates to the iPhone 4 and 3GS allowed you to wirelessly stream music to AirPlay enabled speakers -- or through your home hi-fi system using an Apple Airport Express base station. The iPhone 4S brings in AirPlay mirroring, which allows your massive TV to mimic the screen of your phone without having to manually connect it.
It's great news for gaming fans as you can sit back in your comfy sofa and enjoy all those iOS games on a big screen. Angry Birds on an 85-inch TV, anyone?