A method is disclosed for enhancing the predictability, scalability and cost effectiveness of online advertising with voice over IP connectivity and event tracking technologies. A service provider maintains a list of merchants who have offered to pay for customer VoIP calls to their establishment. The service provider maintains a real time connection with this merchant list and renders an advertisement in a distinguishing way in real time. A potential customer who views this advertisement on a web page may establish a VoIP call session with a merchant by selecting a free click-to-call link on the web page. When the customer places the call, the service provider pays for the call. Merchants in turn pay the service provider for displaying the ads that generated the calls on a price per call, price per impression or fixed fee basis.