You should think of the latest iPhone — which hits the shops on Friday — as a flashy sportscar that has just been given a tune-up. Yes, it looks much the same as it always did, but the real work has been done under the bonnet.

It’s bigger, faster and has better features. But only real gadget aficionados will think it's worth the added expense. Everyone else may decide that an older version, which will be significantly cut in price, will do just fine.

First, Apple’s smartphone has been given an subtle name change: iPhone 3G S. The “S” stands for speed, and Apple thinks that this factor is so exciting that it will convince many to part with their cash.

Apple says that the iPhone 3G S is up to twice as quick as the 3G, able to load web pages quicker and launch applications faster. After a week playing with it, this claim stands up well to closer scrutiny. Especially when the iPhone is connected to wi-fi, the phone is superfast on the web and makes most PCs seem laughably slow in comparison.

And yes, it is bigger. The 3G S comes in 16GB and 32GB sizes, doubling the memory capacity. Music fans will particularly appreciate this, as it will allow them to have thousands more songs stored on their phones.

And yes, the features are better. The camera is upgraded to 3 megapixels and now has a autofocus feature. To focus on a particular part of your shot, you simply tap the screen.

But don’t kid yourself, the 3G S is not a replacement for a decent digital camera, because it still doesn’t have the capacity to zoom. When I asked senior Apple execs why the new iPhone can’t do something so simple, they said that optical zoom technology would take up too much room in its sleek design. The niggles with the iPhone always occur when Apple decide that design is more important than practicality — and this is a case in point.

But it does come with a video camera for the first time. This “new” feature might get a sarcastic slow-handclap from those who may point out that — cough — other phones already have a video camera, and have worked out how to zoom too. Agreed. But the 3G S allows you to scroll through stills from the video by sliding your finger across the screen, and to cut down the video instantly using a “trim” feature.

A more gimmicky added feature is “voice control”, by which the iPhone can react to simple voice commands. You can simply say “Call Mum” the iPhone will react accordingly.

This sounds something out of a sci-fi novel, but it is actually a bit clunky. For example, it easily confused “Play songs by The Killers” with “Play songs by Kelis”. Sometimes I couldn’t work out the right commands. Admittedly people may just learn the right phrases to use, but ideally you want something more intuitive.

After getting a few weird looks from people while I was very slowly and deliberately asking nobody in particular to play music, I decided to stop using voice control. Maybe you will have a higher embarrassment threshold than me.

Almost everything else the new iPhone offers sounds great, but this is a cunning piece of marketing spin. Apple have dealt with a lot of the niggles people had with the older versions. It can finally cut, copy and paste. It has a landscape keyboard for writing email. It can send picture messages. It has the capacity to do “internet tethering”, allowing your PC or Laptop to use your iPhone’s 3G connection and connect to the internet when you’re not in a wi-fi area.

But all of this is part of the iPhone software update, which is available for free on the current iPhone 3G. This means that, if you’re not too bothered about having a fancy(ish) new camera and faster phone, buy the cut-price iPhone 3G. From Friday, the 3G could be hundreds of pounds cheaper and and capable of doing many things the new 3G S will be able to do.

But if you really, truly care about having the latest, and quite frankly, best smartphone on the market — the iPhone 3G S is the one for you.

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