Person-to-person communication on digital networks has begun to play an important role in our daily life. In a ubiquitous networking environment where we will be surrounded by more and more networked devices, real-time communication should be performed using appropriate devices, applications, and network. Moreover, when our situation changes, resources must be switched dynamically without breaking down the ongoing session. In this paper, we present a unified resource switching mechanism that supports network, device, application, and composite switching. Resource switching can be executed even in a session initiation phase because this is designed based on the SIP protocols. The implementation of the prototype and the experimental results are also described in the paper.