Update: click here for full details of the new 3G iPhone

In pictures: the new iPhone and its rivals

In a few hours time, Steve Jobs, Apple's chief executive, will stand up and address a conference in San Francisco at which he is widely expected to unveil the next version of the company's much-lauded iPhone.

In the meantime - as is customary before product announcements from Apple - pundits the world over are busy making their best guess at what he will say.

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"The 3G iPhone will be announced at the World Wide Developers Conference - there really can be no doubt," intones the Mac Rumors website, a reliable source of Apple information.

This seems to be a safe prediction: Mr Jobs has previously indicated that Apple plans to sell a 3G phone; AT&T, Apple's US partner for the iPhone, has announced that it will complete the roll-out of its 3G network this month; and Apple has been busy stitching up deals with carriers in countries where the majority of customers have 3G phones, such as Japan.

But while almost everyone agrees that the new iPhone will use 3G technology to improve internet download speeds, conjecture about other possible features is still building towards its zenith.

One of the most consistently cited is GPS capability, which will mean that the phone will be able to locate itself via satellite and offer a range of so-called 'location-based services', such as the ability to find nearby restaurants and businesses.

The existing model can locate itself, but it relies on mobile phone masts and a process known as triangulation, which is less accurate than GPS.

Several Apple-watching sites have said for months that the next-generation iPhone would have GPS, and over the weekend one of the most authoritative tech blogs, Engadget, claimed to have seen an exhaustive breakdown of the phone's components, including a GPS chip.

Far less certain - though still generating significant grist on the rumour mill - would be a video-conferencing feature that would allow a people to beam images of themselves to their correspondents via a camera mounted on the screen side of the device.

Kevin Rose, the founder of Digg, another tech site, has predicted that the device will be capable of video chat. The French newspaper Le Matin said as much a month ago - though its source was unknown - while Ryan Block, the editor of Engadget, has claimed categorically that the new iPhone has "no front-facing, videoconferencing camera".

There is also a healthy debate about pricing.

Last week a UBS analyst said the 3G iPhone could go on sale for as little as €99 in Europe - though would likely cost closer to £100 in the UK. O2, Apple's UK partner, cut the price of the 2G version from £269 to £169 in April.

The new pricing deal, analysts said, was the result of Apple having struck a deal with operators which will allow the latter to take a greater share of the monthly revenue from iPhone customers, in return for subsidising the device, analysts said.

Rumours of a much cheaper device - in the US, some observers have suggested that the price will drop from $399 to $199 - have in turn sparked speculation that Apple may be preparing to launch two versions - an "iPhone-lite", with fewer features, alongside a more sophisticated model.

According to industry sources, however, the cheaper price will not stem from a pared-down device, but rather a decision by Apple to change its business model - in particular in Europe, where sales of the iPhone have been disappointing, and where it may be willing to receive a smaller percentage of monthly revenues in the hope that more units will be sold.

According to Jupiter Research, fewer than 350,000 of the five million iPhones sold so far were bought in Europe.

Joe Svetlik, news editor of T3, said: "Apple keeps schtum about announcements, but everyone's set on the new device being 3G, and there's also a possibility they might introduce two different sizes - one with a bigger screen - which would the experience of watching a movie much better."

Apple is also expected to reduce the time lag between when the new iPhone goes on sale in the US and when it ships elsewhere.

Today a queue of some 60 people formed outside Apple's flagship store, on 5th Avenue in New York, in anticipation of the launch.

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