The present invention proposes a solution for providing IMS services to users having circuit-switched controlled terminal being not adapted to provide IMS services to the users. In particular, it is proposed, in order to allow IMS to take the full call and service control, to place a user agent being responsible for the user ported to the IMS in a new node type called Mobile Access Gateway Control Function (MAGCF). This new node combines the logical functionality of a cellular switching center and the logical functionality of IMS. Further it is proposed to enhance a user's register, like HLR, to provide also information about the availability of a MAGCF node and about whether a particular user is enabled to use the MAGCF functionality.