Inciar communications method based on IMSI

Method of initiation of a communication IP Multimedia Subsystem for a user who is not registered a priori in the IP Multimedia Subsystem, the method comprising: receiving a communication request from the unregistered user in an application server Initiation Protocol session through an interface with an external network, or receiving an internally or externally generated stimulus requiring the establishment of a communication IP Multimedia Subsystem; assign a control function Call / State Service unregistered user; submit a request for Session Initiation Protocol from the Application Server to the Control Function Call / State Service assigned; and establish the requested communication.