Abstract: A software architecture for a computer telephony server for simultaneously implementing a plurality of messaging applications is provided. The server includes a processor, a memory and a plurality of slots connected to the processor through a high-speed bus, each of the plurality of slots being adapted to receive an interface card for connecting the server to an external resource. The server further includes a session having a thread of execution on the processor and controlling a subset of the memory and a telephone line resource. The call processing behavior of the session is defined by a first user agent which represent a known user of the server. The first user agent includes a first scenario and a first set of properties. The first scenario includes a plurality of event-application pairs, each pair representing a valid event and a corresponding application that is executed when the valid event is detected.