Skype is a universal multi-platform IP telephony application.So anyone with mobile /Desktop Skype application can call their friends /relatives in very low rate when compared to mobile carriers (exception to gulf countries).
They have already developed mobile clients for Symbian and Windows mobile platforms ,but never one for Apple iPhone .And if the rumours are correct , we can expect a Skype iPhone application in the coming week .Currently we have Trufone ,Nimbuzz and Fring offering access to Skype for free . So we expect Skype for iPhone to be free .
Anyways AT&T would be unhappy about the launch of Skype for iPhone .
Download Skype for iPhone ( Will be active after official release )
Download Truphone : Alternative Skype client for iPhone .