A system for tracking telephone calls made in response to advertising campaigns in electronic or other media is provided. The system permits an advertiser to associate specific and distinct telephone numbers with associated advertising campaigns. The system further modifies advertiser-provided information in response to the advertising campaign to which a potential customer responds, and includes the associated telephone number in the modified advertiser information. The system processes telephone calls made to the selected telephone numbers, and provides reports to advertisers of call data associated with the respective advertising campaigns.