This thesis is based on research, design and prototype implementation work done towards defining an Intelligent Network system integrated with Internet functionality and potential services to be provided by such a system. The main driving force behind the project has been an idea to explore the possibility of adding value to services offered by the two most ubiquitous public communication networks of today, by connecting those networks. The goal of the project was to define such a connection and the services that would become possible through its existence. The thesis begins with presenting the background to the project. First of all, it contains the definition and description of Intelligent Networks, as the standard means of providing, in telephone networks, services other than basic connectivity. Further, it defines the Internet and looks at the already existent computer network - telephone network integration systems. In the second part of the thesis, the design of the Internet-Integrated Intelligent Network (DIN) system is laid out. The IHN has been defined using definition methods already standard for the IN, as far as this was possible with regard to the entirely different nature of the Internet. The fundamental role of the World Wide Web Internet application in the functioning of the designed system is shown. Following the research and design work description is an account of the implementation work done to build an IIIN prototype and a group of sample services chosen and implemented to demonstrate IIIN functionality. This account includes a list of demonstration scenarios that have successfully been tested on the system prototype.