San Francisco - In a move that could ring in big changes in the way customers use their mobile phones, internet telephone company Skype will introduce its free software for the iPhone on Tuesday, with versions for other smartphones following in May, the New York Times reported Monday.

Skype already boasts that 400 million customers around the world are using its peer-to-peer telephone system that allows free calls to other Skype members and cheaper rates than other phone companies for calls to landlines and mobile phones.

Porting its system to smartphones would allow users to avoid paying cellphone companies' relatively high charges per minute. But Skype users on iPhone will initially be limited to using the system only when their phones are connected to wi-fi networks, with the software blocked from using the carriers' cellular networks, the report said.