Skype has long been popular a way for customers to place phone calls and video chat at home. But now the program, which was downloaded by an estimated 480 million people world wide, could allow uses to make calls for free from their internet-capable cell phones.Iphone and some Nokia customers can already download the latest version of the program. Vodafone and T-mobile are worried that their already sinking revenues could drop even farther. Our reporter Michael Altenhenne visited the developers of Skype in the Estonian capital Tallinn.