In recent years, machine-to-machine (M2M) communications, which do not need direct interactions from human beings, are booming to meet the fast-increasing requirements of datacentric wireless services and applications. Mobile cellular networks (MCN) and wireless sensor networks (WSN) are evolving from heterogeneous networks to converged networks, in order to support M2M communications. In this article, we investigate and discuss key technical challenges and opportunities for the convergence of MCN and WSN. We propose that the mobile terminals in MCN act as both sensor nodes and gateways for WSN in the converged networks. We evaluated the performance gain, and our simulation results show that better system performance, in terms of throughput, delay, and network lifetime, can be achieved in WSN by using interactive optimization with MCN.