IPhone users will be able to make free phone calls from today as Skype becomes available for the first time on the popular Apple gadget.

Skype, the internet telephone unit of eBay, has more than 450 million registered users. It has been pushing to make its service available on “smart-phones” - such as the iPhone - rather than only desktop computers.

As with the Skype service on PCs, phone calls will be free between Skype users and calls to other landlines and mobiles will cost less than normal network rates.

Scott Durchslag, Skype’s chief operating officer, said: “There’s a pent-up demand. Skype software for the iPhone has been the No 1 request among our users.”

Skype also said that its service would be available on millions of BlackBerry phones in May. It has already announced Skype for Nokia phones, as well as handsets that run on Google’s “Android” software for mobiles such as the T-Mobile G1, and Windows Mobile phones.

As well as the iPhone, Skype will also work on later versions of Apple’s latest iPod Touch, which has wi-fi capability but cannot make cellular phone calls. The iPod Touch released last September has a microphone, unlike the original model. The Skype application will be available free to download from Apple’s App Store today.

Geoff Blaber, a CCS Insight analyst, said: “For Skype it’s an important step. They want to diversify the range of hardware on which you can access the service. The broader the range of products you can use Skype on beyond just a PC, the more attractive it becomes.” Mr Blaber pointed out that Skype calls could be made only on iPhones and iPod Touch devices connected to the internet through wi-fi. This means that using Skype on the iPhone is likely to be limited to use in homes and public areas where wireless connections are available.

This limitation seems to have convinced O2 , the operator that has sole rights to the iPhone in the UK, to allow British users access to the new Skype application. An O2 spokesman said: “We understand [Skype] have designed this to work solely over wi-fi. We have not blocked the application and, if it is available in the App Store, it will be available to our customers.”

Phone operators have blocked other voice-over-internet services that run on mobiles in the past, but Mr Blaber said that Apple allows network operators very little involvement in the making and distribution of their devices, which could mean that O2 had little choice but to accept the feature.

Analysts said that many users were likely to download and use Skype because it was so deeply integrated with the iPhone. One advantage is that it allows subscribers to access phone numbers in their existing iPhone contact lists so that they do not need a duplicate address book.

Some critics complained about the usefulness of the new Skype product because the software must be running on an iPhone for a user to receive calls. A Skype spokesman said that the service worked in the same way on desktop computers, needing to run in the background after a PC was switched on for calls to be received. He added that if a call was made to an iPhone and the Skype application was not running, an indication showing that calls had been missed would show up.

Several other companies, such as Truphone, have already offered software that can turn the iPhone and iPod Touch into an internet telephone, but this will be the first to offer Skype functionality under the Skype brand.

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