A system and method for analyzing audio signals sampled from a telephone line during moving sample windows in order to detect indicia of three way calling attempts. The system and method sample audio signals on the telephone line, sort the sampled signals into a profile of levels for the sampled audio signals, and monitor the profile of sampled audio signals for reset and reference conditions. Reset conditions are pulse patterns identified from sampled audio signals that are inconsistent with patterns generated by three way call events. Reference conditions are pulse patterns identified from sampled audio signals that are consistent with patterns generated by three way call events. A sampling window and its associated profile are reset when reset conditions are detected. The profile is tagged as a potential three way call event when reference conditions are detected in a sample profile and no reset conditions are detected over the selected sampling interval (sampling window). In the preferred embodiment, an indication that a three way call attempt is occurring is generated when two consecutive tagged profiles are detected.