As anticipated, Apple announced its latest iPhone last week, but it turned out to be a seriously souped-up iPhone 4 rather than a completely new iPhone 5.

Dubbed the iPhone 4S (following naming convention of the similarly upgraded iPhone 3GS from 2009), the new smartphone looks just like the old iPhone 4, but is reckoned to be twice as fast overall, with seven-times faster graphics.

The iPhone 4S also has a better camera than its predecessor, capable of taking 8-megapixel photos and shooting high-definition video at 1080p.

Apple has also upgraded the lens in the iPhone 4S — a component all too often ignored by smartphone manufacturers, which is why their images are seldom as good as a dedicated digital camera with a lower resolution.

Judging by the sample images Apple has published, the iPhone 4S should make a more than adequate replacement for a digital compact camera. The fact that it lacks a zoom lens is perhaps compensated for by the fact that people are more likely to carry a smartphone with them all the time, too.

The other notable hardware improvement is that rather than offer two separate versions of the iPhone for use in the US and the rest of the world, the iPhone is now a ‘world’ phone that works everywhere.

In technical terms, this means it will work on both US CDMA networks and European GSM/3G networks, although it will need an appropriate contract with a provider.

This feature is unlikely to affect UK users travelling to the US, but it does mean that US users will be able to use a cheap PAYG SIM for calls rather than pay extortionate roaming rates for their home CDMA provider.

Many of the other new features offered by the iPhone 4S (including free text messaging to other iPhone users) will also be available to iPhone 4 and iPhone 3GS users this Wednesday, which is when Apple launches its free iOS 5 iPhone software update.

One feature that will remain an iPhone 4S exclusive, however, is the impressive voice recognition technology called Siri.

As well as offering speech-to-text conversion for composing e-mails and text messages, along with the existing ability to make telephone calls based on spoken “Call [name]” commands, Siri also offers much more sophisticated options.

Not only can Siri can read out emails and text messages using a computer synthesised voice (and type a reply based on what you say), but it can also perform internet searches in response to spoken questions.

So, for example, if you ask what the weather is going to be like tomorrow, Siri will speak a reply and display relevant on-screen information. Similarly, you can ask Siri to set a reminder about someone’s birthday and will configure an appropriate alarm.

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It’s too early to say how useful Siri will be, but the applications are obvious for anyone who spends a lot of time driving with a hands-free kit.

The iPhone 4S goes on sale this Friday, with prices for an unlocked SIM-free model as follows”

  • iPhone 4S 16GB: £499
  • iPhone 4S 32GB: £599
  • iPhone 4S 64GB: £699

O2, Orange, Three, T-Mobile and Vodafone are all offering the iPhone 4S with contracts too, but you’ll need to take a look at their sites to see the various deals on offer.

The iPhone 4S probably isn’t a compelling upgrade for iPhone 4 users (particularly once iOS 5 is available), but older iPhone owners will probably appreciate its faster performance and better camera.

That said, the iPhone 4 has also received a price cut, so it may be a more tempting — and cheaper — upgrade option for anyone still using an iPhone 3G or 3GS.