For multiple registration of a multimodal communication terminal (MKE) via at least one access network in an IMS-based service communication system in a mobile and/or convergent communication system, where the multimodal communication terminal (MKE) is registered for at least one communication service via a first access network (WIAN) in at least one service control unit in the IMS-based service communication system (S-CSCF), a registration message with an access network identifier (ZK) is produced and is transmitted to the at least one service control unit (S-CSCF) in the IMS-based service communication system. The at least one service control unit evaluates the access network identifier (ZK) and takes it as a basis for performing further registration of the multimodal communication terminal in the IMS-based service communication system (S-CSCF).