can somebody give me an idea as to how do i go about developing a C++ application with capabilities of calling a number, answering calls etc.

Under Windows, you want to use either RAS, which is pretty high level and easy, or TAPI, which is harder but gives you more control and information.

VC++ comes with sample code for both, those will get you going in the right direction. If this isn't Windows, then someone else can chime in on how to get started...