I would like to share my positive experiences with you. Iím using a sample program providing by Ozeki VoIP SIP SDK to develop chat program. I have found it during my research as I needed some help. With the help of this sample program I can easily implement text, audio and video chat programs and it doesnít require a long period of time. Iíve tried its support and it answered me very fast.
You can use different developer environment such as: Microsoft Visual Studio 2010, Microsoft . Net Framework 3. 5 or 4. 0, Flash builder 4. 5 or other equivalent IDE or Flash player 10+.
If you are interested in this kind of communication technology, you can find the site here: www. voip-sip-sdk. com/p_96-winforms-dtmf-ivr-voip. html
I hope I could help you a little!
All the best,