In Apple's case - about $200BN or more. Anyone could build an iPhone. The proliferation of other platforms (Android, Windows, Ubuntu, ...) proves it. However, nobody but Steve was thinking out of the box at that time. It was just an idea (with a brilliant execution, admittedly).
Modern design with multitouch and capacitive screen, perhaps. First touchscreen phone was the IBM Simon in the mid-90s, and my Kyocera 6035 was one of many Palm/phone hybrids that predated LG by years. There were also Symbian and Windows Mobile PDA/phones.