The objective of the Intelligent Network (IN) concept is to rapidly and flexibly add new services without upgrading the complicated switching systems. To realize that concept in the real telecommunication system, the systems must have an environment for the creation of new services and an architecture for execution of those services. This paper proposes an environment for service creation in advanced telecommunication systems such as the IN. The service creation environment provides means to verify the new service specifications and to create executable specification. To facilitate the verification as well as to model the system resources, the service specifications are formally described by means of High-Level nets, Coloured Petri nets (CP-nets). Specifying services in CP-nets gives the capability for modeling many kinds of systems resources over the network. Especially colour plays effective roles to define both the executer of services and resourses clearly. Since IN architecture allows customers to define their own services, it is difficult to verify the services defined by different customers. Therefore, it is important to define the customers services formally at the specification level. The verification method in this paper is based on the pure net analysis technique. It is, however, extended to handle CP-nets. A customized service is verified for the integration with other services and with other customers' services. The verified services are called Service Scenarios. A software architecture in which services can be executed is also discussed. The system consists of Scenario Database, Scenario Interpreter, and Functional Execution. By simulating the service scenarios, the customized services are executed.