QuteCom (previously called OpenWengo) 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, and is compatible with any SIP provider.
- Full SIP compliance.
- Provider-agnostic. It doesn't matter who provides the phone service to the call recipient.
- Allows users to send SMS messages.
- NAT transversal.
- Cross-platform support.
- QT-based GUI.
- Chatting with MSN, AIM, ICQ, Yahoo, and XMPP users.
I like it!