If you wish to call someone without using minutes on your iPhone's cellular plan, the Skype Voice Over IP (VoIP) application for the iPhone enables you to instant-message and call anyone who has a Skype account for free as well as call users who don't use Skype if you purchase a calling plan, according to the official Skype site. As of July 2010, the Skype application is available for free in the App Store on your 3G iPhone and can be used by accessing your phone's cellular network or a WiFi connection.