New Gadget 2011

The phone is expected to go on sale from all five UK networks from 14 October, though none was able to give details of pricing. The Guardian understands that no one knew precisely what was coming until it was unveiled.

Apple also said that a new version of its "iOS" software, iOS 5, to run existing iPhone 4, iPhone 3GS and iPad models will be available from 12 October, bringing its "iCloud" system which synchronises pictures, documents and user video across devices without needing a PC.

While the rumour mill � and the name of Apple's software � had led many to expect that the phone would be called the "iPhone 5", Philip Schiller, the head of marketing, demonstrated the 4S and insisted that it was a complete overhaul of the iPhone 4 released 14 months ago.

A key element in the iPhone 4S is a "voice assistant" called Siri which Scott Forstall, head of the iOS division, demonstrated. It answered complex queries asked by voice such as "what's the weather like today?" and responded in real time with a synthesized voice.

"There's so much you can ask. Compose and dictate emails, ask questions about the weather, stocks, set timers. It's not perfect, but there's a huge amount it can do," said Forstall.

The launch was the first for Apple, the highest-valued company in the world, without Steve Jobs as chief executive after he stepped down in August.

Apple is seeking to stay ahead of its South Korean rival Samsung, which is challenging Apple for the crown of the company selling the mostsmartphones worldwide. The two are expected to be neck-and-neck when figures for the third quarter, to the end of September, are announced. The majority of Samsung's smartphones run Google's Android software.

Apple is aiming to bolster its position in the mobile business, where Cook pointed out that despite its position in the smartphone market it only has 5% of the total market by volume, by targeting the fast-growing Chinese market as well as European and US buyers.

The iPhone 4S includes the A5 processing chip also used in the iPad 2 released earlier this year, making it significantly faster than its iPhone 4 predecessor. Schiller said that the antennas � the subject of a bitter row when some customers claimed that the external antenna led to worse reception � have been redesigned to improve call quality. The camera had also been improved compared to the iPhone 4.

One other change is that the phone will work on any phone network in the world through the inclusion of chips which boost compatibility.

Speaking in the room where ten years before Steve Jobs launched the iPod � the music player which revived Apple's fortunes and helped it gain a dominant position in consumer electronics � Cook said that "I consider it the privilege of a lifetime to have worked here almost 14 years."

Apple also updated two of its 10-year-old iPod line, the internet-enabled iPod Touch and the miniature iPod nano, which will now be offered in watch form � something that a number of Apple fans had demanded last year when it was released. But the "classic" iPod and the tiny "shuffle" were not mentioned, though they are still on sale.