A system and method for analyzing information associated with voice calls placed during a telephone number advertising campaign is described. The system receives information characterizing voice calls to advertiser telephone numbers and information from advertisers such as information about the outcome of the voice call (e.g., conversion information). The system correlates the voice call information with the advertiser information and generates reports based on the correlated information. The system can perform or enable the performance of other actions based on the correlated information. For example, the system may modify an ongoing advertising campaign based on an analysis of the correlated information.