The SIP Switch is a Web application which allows you to use multiple SIP accounts on the same phone. This lets you use the call plans of different VoIP companies (using SIP) with one IP phone device. It does the third party SIP registration so you can receive all your calls on the sipswitch account. On dial out, you can set prefixes to make your outgoing calls with such or such provider.
Mediastreamer is a portable C library that allows you to create and run audio and video streams. It is designed for any kind of voice over IP applications. It features RTP connectivity, audio codecs (Speex, iLBC, G711, GSM, and AMR), video codecs (MPEG4, H263, H264, and Theora), sound card I/O, wav file streaming, webcam video capture, echo-cancellation, conferencing, parametric equalization, and various other utilities. It has a modular design that makes it extensible through plugins. This is the media-streaming component of linphone, a GPL SIP video phone.
VoxForge collects transcribed user-submitted speech audio files (collectively called a "speech corpus") to create acoustic models for use with speech recognition engines such as HTK, Julius, ISIP, and Sphinx. The current focus is on collecting audio to create acoustic models for command and control applications on a PC, and for voice over IP telephony speech recognition applications, i.e. IVR (Interactive Voice Response).