A solution is provided that integrates external services with existing PBX services to provide new features to the PBX without having to update the PBX. To provide the external services, an external application server establishes a Computer Telephone Integration (CTI) channel with the PBX in order to register for one or more events that occur for a communication session controlled by the PBX. When one of the events occurs, the PBX sends a token containing information regarding the communication session and a media server associated with the communication session. The external application server uses the information in the token to provide an external service, via an external application, to a media stream of the communication session. In one embodiment, the media stream may be sent to that external application that provides the service to the communication session.