Ekiga or Gnome Meeting works as an Open Source soft-phone, video conferencing tool and instant messenger on VoIP technology. With interoperability and HD sound quality, this chat client establishes itself as a viable player in the VoIP world.
Prices are not that high when one can see that the calling is done in DVD quality. The service provider remains at your choice and SMS is a possibility provided your network supports that.
Within a sleek interface you will find options like call hold, call transfer, call forwarding and DTMF. IPv6 and audio/ video capture support are still in experimental mode but everybody is eager to notice the difference.