Build windows application based on VOIP technology

Project Name is "Communication between two business platform " I am going to build window application using c# or c. The main core is to calling and receiving function. This system has three type of people. One is caller. Second is operator(middle person) Last one is receiver. Let me explain about logic. The caller calls number to operator on mobile phone. The operator receive incoming calls on windows app(i am going to develop this app). Then the operator patch this call to specific user ( last one receiver) Finally , caller and receiver can talk each other via mobile phone Below is final requirement what i am going to do 1). Members of the public call a dedicated number looking to get information about a business or service. 2). Operator receives the incoming call and searches the database for the callers enquiry. 3). As operator get information after searching database, operator can either give this information to the caller or the callers incoming call is patch through to the telephone number derived from the database query thereby connecting the caller and that business directly. 4). The database will comprise of the following form fields: street, area, town, state, city, road, address. business name, business type e.t.c 5). Database is to be searched using keywords from the caller. 6). the system can be on a network or standalone. 7). in order for busineses to advertise on the system, they can also call the same number and be forwarded to the right department.