Active competition in the telecommunications industry has caused a dramatic shift in focus for public network operators. Service designers need to be able to easily and rapidly create services according to the customer’s requirements. This is achievable by using Intelligent Networks (INs). Two primary goals of service development under the Intelligent Network paradigm are rapid service crcation using new software technologies and the minimisation of service development costs through switch vendor independence. This thesis examines the development of an IN architecture and the deployment of two call control services on it using the ITU-T Service Independent Building Block (SIB) methodology. The services are deployed on a narrow-band Excel switching platform. Various aspects of the IN Conceptual Model (INCM) are examined with a particular emphasis on the middle two planes: the Global Functional Plane (GFP) and the Distributed Functional Plane (DFP). Representations of these planes are designed using the ITU-T Specification and Description Language (SDL) [SDL89] and implemented using Telelogic’s SDL Development Tool (SDT). SDL provides capabilities to allow logical structuring of the INCM into its constituent entities, the modelling of communication between these entities and the processing within them. The Intelligent Network paradigm was developed with a view to extendibility. Two call control services, Ringback and Group Call Pickup, are implemented using the SIB methodology. Further services may be created by rearranging the order of execution of the existing SIBs or, if necessary, by adding new SIBs to the architecture. Given the demand for multimedia applications to run on top of emerging broadband networks it is becoming increasingly more important for network operators to study the enhancement and evolution of their IN service platforms in order to cope with new customer requirements. TINA is the leading architecture for multimedia service control and delivery, which defines an emerging open service platform. Migration from IN to TINA is explored in this thesis by considering two individual paths of migration. The first path involves the replacement of the IN service control and management elements (SCF, SMF, SDF) with appropriate TINA Computational Objects while the switching elements (SSF, CCF) remain IN compliant. As there is no one-to-one mapping of IN functional entities to TINA computational objects, an Adaptation Unit is required to facilitate interaction between the legacy IN entities and the TINA Computational Objects. The advantage of this step is that it is possible to keep the investment of deployed IN SSPs while taking advantage of TINA service modelling. The second step involves the introduction of TINA into the switch. In this approach the switch and its switching capabilities may be viewed as a TINA object in itself. Interworking between IN and TINA (as a step towards full migration to TINA) yields a much richer service platform. This service platform facilitates the creation of services that incorporate both IN and TINA features. A TINA service may use pieces of IN functionality and IN services may also use TINA functionality. It is possible to invoke these hybrid services from either a PSTN or a TINA terminal. Three hybrid IN/TINA services were designed to demonstrate the increased resources available to the service designer using such a platform. A user connected to the IN switch invokes the Freephone Service. This service uses a TINA database to convert the 1-800 number to an extension number. The call is then connected using IN switching functionality. The Audio Video Conference, uses TINA computational objects to set up a video stream between participating users while the audio connection is handled by the IN switching functionality. This service is invoked from a TINA terminal. A user connected to the IN switch invokes the Ringback Service but it runs in the TINA domain using both TINA and IN functionality. Therefore, as well as presenting an application of the IN technology, this thesis proposes possible steps towards migration to the TINA architecture.