An iPhone can be turned into a VoIP phone simply by downloading any of the VoIP apps available on the Apple App Store. The iPhone can then be used to make calls using a Wi-Fi network, even without a mobile connection.
Skype is one of the most popular VoIP apps available for the iPhone. In addition to making phone calls, Skype also supports videoconferencing and instant messaging. There are alternatives, such as Fring and iCall. VoIP can be an affordable alternative to conventional mobile plans, especially for those who have constant access to a Wi-Fi network at home or in the office.