This TR provides a study of the service experience and suggested service requirements for IP Multimedia System (IMS) Centralized Services (ICS). ICS enables the delivery of IMS based services to users regardless of the attached access network type; e.g. CS domain access or IP Based Access Networks. Service continuity between access networks is also considered. User and service provider perspectives are considered along with service scenarios as the basis for identifying service requirements. Based on the previous considerations, service requirements are identified and conclusions are drawn.