In one method and apparatus for blocking unwanted calls in a callback system, parameters associated with a callback request (e.g., the user device to which the call is to be directed, the IP address from which the request originated or an identifier of the source computer from which the callback request originated, the party from whom the call is requested) are tracked for each call. A decision to automatically block the requested callback is made based on one or more criteria based on a combination of these parameters, which may be a total over a period of time. In a second method, one or both of the parties to the callback is queried as to whether the callback is unwanted and, if so, one or more parameters associated with the request are blacklisted.