OfficeSIP Softphone and Messenger

OfficeSIP Softphone and Messenger are two enterprise VoIP SIP clients written in C# in .NET Framework. The SIP clients make use of Microsoft UCC API SDK, ensuring the highest quality of audio and video. Compatible with Office Communications Server.

See also open source, cross-platform:
1) simple messenger Brief Msg at http://briefmsg.org
2) MUVConf is a multi-user video conferencing, see demo video http://youtu.be/YrBU-Aqtvrk, download https://code.google.com/p/muvconf/downloads/list

Today’s small-to-medium-sized (SMB) businesses and large enterprises are saving on their monthly communications costs by making one simple decision: to switch to a VoIP service solution from their old, outdated Plain Old Telephone Service (POTS). By choosing a new VoIP service, these companies enjoy the flexibility, reliability, call features, and audio quality that only a VoIP service can provide. Plus, they cut their phone bill by up to 70%!