QuteCom

Wikipedia says QuteCom (previously called WengoPhone) is a SIP-compliant voice-over-IP client that allows you to speak to other users of SIP-compliant softphones at no cost. It also allows users to call landlines and cell phones, send SMS text, and make video calls. You can use it with any SIP provider.

QuteCom is similar to:

AOL Instant Messenger, Ekiga, Skype, Yahoo! Messenger

QuteCom is used for:

VoIP

Who uses QuteCom:

administrative worker, artist/illustrator/designer, business user, home user, office worker, project manager, researcher, retailer, sales professional, service professional, system administrator