News that Apple has upgraded the iPhone ahead of its US launch next Friday (June 29) helped add $2 billion (£1 billion) to the market value of the company in early trade today.

In a statement that seemed designed to counter mounting fears that the iPhone would be hampered by a lacklustre power supply, Apple said that the finished gadget will feature up to eight hours of talk time, six hours of internet use, seven hours of video playback or 24 hours of audio playback.

Previously Apple had specified five hours of talk time - though some technology commentators had put the figure as low as 40 minutes.

The device, already dubbed “The God Machine” by Apple aficionados, will also feature up to 250 hours – or more than 10 days – of standby time, the company claimed.

The news helped send the shares up more than 2 per cent in New York.

The company added that the entire top surface of the iPhone has been upgraded from plastic to optical-quality glass “to achieve a superior level of scratch resistance and optical clarity”.

The move follows reports that the iPhone's glossy casing scratched too easily and that its touch-screen technology is fiddly to use. Some reports have suggested that as many as one in five iPhones could be returned because of faults.

The speculation seemed to mirror consumer complaints over the original iPod Nano, a miniature version of the hugely popular digital music player. After facing a storm of criticism from disgruntled Nano owners, Apple completely remodelled the product last year to give it a durable aluminium shell.

The last-minute revisions to the iPhone’s specifications will notch up speculation that Apple’s engineers are being stretched to the limit in readying the device for its launch date.

In April, Apple was forced to delay its next-generation operating system to free up staff to ensure the timely release of the iPhone, judged by analysts as by far the more important product.

Leopard, the latest version of the Mac OS X line, was pushed back until October, from June. Analysts expect the move to hit Apple's software revenues by about $150 million (£75.8 million) this year and said that there could be a knock-on effect on sales of its computers.

The decision to divert resources to the iPhone underscored the expectation attached to Apple's first foray into the mobile sector. David Bailey, the Goldman Sachs analyst, said: "Although the push out of Leopard is not ideal, we view iPhone as the driver of the next leg to the Apple growth story."

In May, Apple unveiled an upgrade to its Apple TV device, a set-top box that wirelessly streams video content from computers to TVs, introducing a model with a 160 gigabyte hard drive, four-times larger than previous versions and enough to store up to 200 hours of video.

The upgrade, just 141 days after Apple TV was launched at the group's Macworld Expo in San Francisco, raised further question marks over whether Mr Jobs was satisfied with the original product.

Observers have suggested that Apple TV will struggle until the device supports high-definition pictures, with some pointing out that in terms of picture and sound quality consumers would be better off opting for a humble DVD player.

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