* Compatible with Windows 98/Me/2000/XP/2003
* Supports work behind NAT/Firewall (STUN is used)
* G.723.1, G.729, G.711, GSM, iLBC codecs
* Voice Activity Detection (reduces data traffic sent during silence periods)
* Automatic adjustable Jitter buffer
* DTMF tones (can be integrated with voice mail or other tone driven system)
* Registers with SIP Registrar
* Supports SIP Outbound Proxy

Demo version is available here:
http://www.duxoft.com