MizuPhone is a free SIP softphone for windows which lets you make VoIP/SIP calls to users anywhere in the world using any VoIP service provider, SIP server or your own PBX.

Features:
-Easy to use, zero-touch configuration
-Multiple profiles, multiple lines
-Superior voice quality with audio enhancements: Echo canceller (AEC), Automatic Gain Control (AGC), Voice Activity Detection (VAD), Packet Loss Concealment (PLC), automatic QoS, Noise Suppression
-audio codec: G711, G.722, G.723, G726, G729, GSM, iLBC, L16, Speex, wideband and ultra-wideband
-Video Codecs: MJPG, MPEG1, MPEG4, Theora, H263, H264
-Networking autoconfiguration to bypass any NAT and router using UPNP, STUN, ICE, firewall and NAT detection
-Intelligent P2P based network path detection (can call other users even if the server is down)
-VoIP tunneling and encryption bypass any firewall or ISP VoIP blockage
-Call and chat history with voice and video recording
-Remote Desktop and file transfer over VoIP (compatible with any SIP server)
-All standard Class5 SIP features are supported such as voicemail, call forward, call transfer and conference calls (conference are working even without server side support)
-Customized/branded versions are available with support for all major VoIP servers such as Cisco, Asterisk, MizuVoIPServer, Huawei, OpenSER, OpenSwitch, FreeSwitch, Brekeke,VoIPSwitch, Awaya, Siemens and Nortel.