Freeware: Mwi

TERAVoice Server 2004TERAVoice is a high-performance telephony platform for Windows that can implement any type of telephony application like voicemail, automated attendants, voice menus, waiting queues for call centers, H.323 to PSTN gateway and custom IVR applications.

3CX VOIP Phone for Windows 1.0Free VOIP / SIP phone. Use your PC as a phone. Works with any SIP/ VOIP provider/ phone service. Easy to use interface to transfer, forward calls or set-up conference calls.

3CXPhone FREE VoIP Phone for Windows 4.0Free VOIP / SIP phone (softphone) for Windows. Use your PC as a phone. Works with popular VOIP providers and SIP PBX's (including 3CX Phone System). Easy to use&light weight. Full version, not a lite version! Free download from http://www.3cx.com