Recent mobile environment has various types of smart things which are opportunistically adjacent to the surrounding areas of mobile phones. However most of applications in the market are just statically bound to specific model of designated manufacturer which were chosen in development phase, so they are not interoperable with heterogeneous things even though they have similar functionalities. To optimize utilization of smart things residing in each user's personal pervasive environment, IoT mashup application is required which dynamically discovers heterogeneous things, downloads needed software module at runtime, and provides mash-up application to the user. In this paper, we designed and implemented IoT Mashup Application Platform that supports smartphone-centric discovery, identification, installation, mashup and composition of the pervasive smart things. Furthermore, by decoupling the roles of actors in IoT ecosystem utilizing functionally abstracted thing interfaces, the platform provides benefits to each actor — thing manufacturers can maximize compatibility of their products, application developers can concentrate on their own business logic, and the end-users can select which smart things would be actually used for the composition.