Two websites are vying to offer the first commercial service for unlocking Apple's iPhone so that the device can be used outside the US in Europe and elsewhere.

The "unlocks", which would be bought as a piece of downloadable software over the internet, will enable the phone to be connected to any network in "multiple countries", the sites claim.

So far the iPhone is only available in the US on AT&T, but in the past two months a number of hackers have posted details on the internet of how to unlock the phone, meaning that it need not be tied to any particular network.

The latest offerings differ in that they do not require any sophisticated equipment - only a single download - and will appeal to owners of the phone in Britain and elsewhere who have bought the phone in the US and are keen to insert their existing SIM card.

iPhonesimfree, which appears to be closest to introducing a service, posted a comment on its site today saying that it was hoping to release the software "in the next 48-72 hours". The unlock would enable the iPhone to function normally, but be connected to a British network.

"We have both voice and data extensively in multiple countries, using various different carriers and have found no problems," iPhonesimfree said.

Uniquephones, based in Belfast, an established site which offers unlocks for a range of handsets, has posted a video which purports to demonstrate its software, but when pressed by Times Online to unlock an iPhone that had been purchased in the US, declined.

The site, which said it will charge $50 (£25) for the service, has recently received a letter from a law firm representing AT&T, the official network for the iPhone in the US, "presenting issues such as copyright infringement and illegal software dissemination". It was still taking legal advice, a spokesman said.

Neither unlocking a phone nor selling a service to unlock a phone is illegal in the UK, according to Ofcom, although a customer who has a contract and unlocks their phone so that it can be taken to another network may be breaching the terms of the contract, the regulator said.

That situation is unlikely to arise in the case of the iPhone, however, because the device can be bought in an Apple store - for either $499 or $599 - before any contract is signed. In other words, the market for unlocking iPhones will be those people who have bought the device without a plan and want to insert their existing SIM.

There are numerous reports of Britons who have either bought the device on eBay, or asked a friend to buy one in the US and bring it back.

Jeremy Plant, a 46-year-old publisher from Elstree, Hertfordshire, was among those excited British iPhone owners who were anxious that the sites introduce their service.

"I've already got mine to work as an internet browser and a music player, but obviously I want it to work as a phone as well," said Mr Plant, whose friend bought him an iPhone in the US two weeks ago.

Neither Apple not AT&T have commented publicly on unlocking, but the issue is likely to provide a major headache for O2, which is widely reported to have been awarded the contract to release the phone in the UK.

A readily available unlock would mean that O2 will fail to reap the rewards of its exclusive contract - for which it is understood to have paid handsomely.

Lawyers said that O2 would be pushing to have a clause inserted in its contract with Apple that made it the "sole and exclusive distributor" of the device.

"That way Apple could be stopped from selling the device on its own, and one could prevent the situation of a person owning an iPhone without a contract," Tom Wheadon, a partner in telecommunications law at Simmons & Simmons, said.

iPhone: from sale to hack

June 29: iPhone goes on sale in the US

July 2: First reports of an iPhone hack surface in internet forums, one hacker - 'gj' - claiming: "i'm pretty sure I know how to do it"

July 6: Unnamed hackers claim to have discovered the iPhone's root password - 'dottie' - but it is not immediately clear what its use is

July 6: Renowned hacker 'DVD Jon' completes the first successful hack, but once unlocked, the device only works as an internet browser and iPod, not a phone. The procedure also requires sophisticated equipment

July 23: A group of security researchers demonstrate how to take control of the phone using its internet connection, and get it to forward on personal information, including text messages and contact numbers.

Aug 25: A New Jersey teenager, George Hotz, releases details of a hack, having spent 500 hours tinkering with the software and rewiring the device with a soldering iron

Aug 29: Two websites claim to be 'days away' from releasing a commercial iPhone unlock service for $50

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