From iA wiki
Also known as: teleconferencing, Voice over IP (VoIP)
Internet Telephony is voice chat or real-time audio over the internet. Sometimes protocols for Internet Telephony are used in conjunction with video for videoconferencing. Net telephony services are also being introduced and offered by the Big Boys.
- Skype - free, easy to use internet phone with conference call feature
- Speak Freely - a cross-platform telephone system with encryption, an answering machine, and selectable compression. GPL-licensed.
- CoolTalk - originally packaged with Netscape 3.0, includes whiteboard and text chat features. Still free and available for several operating systems.
- Roger Wilco - a free multi-user client, ideally for computer gaming.
- Net2Phone and DialPad - commercial services that allow calling from the Internet to a normal phone instead of Internet-to-Internet. Net2Phone users can call other users for free (and DialPad may as well).