Skype is a proprietary software application that offers free Skype-to-Skype calls and low-cost local, national and international calls to both traditional land-line telephones and mobile phones. Additional features include instant messaging, texting, call forwarding, and video conferencing.
Skype now also a premium version that has Group Video Calling.
On Skype for iPhone, you can make free video calls to other devices with Skype installed, over both WiFi and 3G.
Visit http://skype.com/m for Android and Blackberry versions of Skype.
For webOS phones: https://developer.palm.com/appredirect/?packageid=com.palm.app.skype
Available also as portable app: http://portableapps.com/apps/internet/skype_portable
