SIP softphone - graphical client

 Linphone is an audio and video internet phone using the SIP protocol. It
 has a GTK+ and console interface, includes a large variety of audio and video
 codecs, and provides IM features.
 .
 The main features of linphone are:
   - a nice graphical interface;
   - it includes a large variety of codecs with different quality / bandwidths;
   - it uses the well-known and standardised SIP protocol.