A computing infrastructure where "everything is a service" offers many new system and application possibilities. Among the main challenges, however, is the issue of service integration for the application development in such heterogeneous environments. Service integration has been considered by major middleware as a user centric approach as it responds to user requests and needs. In this article, we propose a novel way to integrate services considering only their availability, the functionalities they propose and their non functional QoS properties rather than the users direct requests. We define MySIM, a spontaneous service integration middleware. MySIM integrates services spontaneously on an event based mechanism and transparently for users and applications, extending by that the environment with functionalities. We developed a prototype as a proof of concept and evaluated its efficiency over a real use case.