In this paper, we propose a Software-Defined Networking (SDN)-based mobile networking approach with two kinds of controller models. The proposed approach keeps the legacy mobility control plane integrated with SDN, thus being able to realize flexible and scalable cellular networks based on SDN, while supporting enhanced mobility management on the utilization of legacy mobility control plane. That is, such a partially-separated mobile SDN architecture can increase the flexibility of mobility management while maximizing the utilization of the deployed networks, without stripping all the mobility-related legacy equipment from the network. We describe the applicability of the presented approach with exemplary use cases that can be effectively achieved or flexibly implemented over the proposed models. Enhanced performance and implementation challenges are finally presented and discussed.