The world is witnessing a rapid growth in mobile communication, and operators have been forced to handle network traffic more resourcefully. Many works point to the use of Software-Defined Networking (SDN) as an enabling technology to overcome current limitations, making possible upcoming 5G networks. In this paper we discuss how the OpenFlow protocol can be integrated into existing Long-Term Evolution (LTE) networks, going through state-of-the-art solutions and highlighting open issues. We also introduce a novel OpenFlow module for ns-3 simulator, allowing reliable simulations of LTE-SDN integrated networks, as illustrate in a case study example.