Skype has confirmed that iPhone users will be now be able to use its internet telephony service. The firm's native voice over internet protocol (VoIP) application - Skype for iPhone - will be available for download from Apples iTune store on Tuesday. The new service will allow users to make free calls to Skype users, but will charge for calls to other numbers. The UK's first Skype capable handset was launched by Mobile operator 3 on 2 November 2007. Rival applications from Fring and TruPhone are already available for the iPhone. Unlike traditional mobile calls, which are transmitted over a cellular network, VoIP turns your voice into data and sends it over the internet using a wi-fi network. This means the only cost to the user is for sending internet data; for iPhone users this means no cost at all, as they get unlimited internet access within fair usage limitations. VoIP firms will levy a charge for users making calls outside its user base. In the case of Skype, while calling another Skype user will be free, calling an actual phone number via the service will incur a cost. Iphone users will not be able to make Skype calls, either to Skype contacts or to landlines, over the mobile network, something users of Skype on the UK mobile network 3 can do. Watching the pennies Many of Skype's other features - such as video conferencing and the ability to receive a second Skype call - have been left out, although the firm did not rule them out in the future. "We're considering video carefully but we have a really high bar on the quality," said Skype's chief operating officer Scott Durchslag. "If we do it we will have to do it incredibly well." Mr Durchslag said he had high hopes for the application. "The number one request we get from customers is to make Skype available on iPhone," he said. Skype plan to launch a service for BlackBerry users in May.