Monitoring multiple telephones using computer

I am a final year student at Mekelle universty here in Ethiopia and I’m trying to develop a software that controlls the call status of multiple telephones from a single PC as a senior project .What I have found it difficult is connecting multiple telephones to a single PC.Though I have decided to use a PBX I don’t know whow to interface it to the PC.Can you comment something on this problem?Remember I am in the third world were there is a high scarcity of reference and resource.