The present invention faces the problem of network scenarios where there is no user differentiation, and where sessions established through an IP Multimedia Subsystem always proceed in the same way regardless user categories and regardless whether a user has accessed through a fixed or a mobile network. To this end, the present invention provides for a new method for dynamically configuring a Proxy Call Session Control Function of the IP Multimedia Subsystem from a Policy Control Rules server responsible for installing control rules to authorize media flows at an entity in the bearer layer. This entity in the bearer layer may be a Policy and Charging Enforcement Point of a PCC architecture, whereas the Policy Control Rules server may be a Policy and Charging Control Rules of the PCC architecture.