sessions conducted over a communications network, such as a voice over Internet protocol (VoIP) network, that employs a session initiation protocol (SIP). The method includes receiving a subscription request from a third party subscriber, the subscription request identifying a targeted user to be monitored, monitoring communication sessions in which the targeted user is a participant, to detect SIP events corresponding to state transitions associated with the communication sessions. A system for facilitating surveillance of a targeted user includes an application programming interface (API) operable to receive a subscription request from a third party subscriber, the subscription request identifying the targeted user, wherein the third party subscriber is not a participant in the one or more communication sessions, and a SIP events monitoring module operable to detect one or more predetermined SIP events associated with the communication sessions based on the subscription request and notify the third party subscriber of the detected SIP events.