Wired, wireless, and mobile networks are converging to an all IP heterogeneous network with immense complexity. The underlying access network technologies have a high variance of characteristics. The diversity of multi-mode devices is growing rapidly. These factors have a significant impact on the services running on top of this broad range of different access network technologies. To develop next generation services and solutions for next generation heterogeneous networks, researchers need an adequate environment. This paper presents a "mini" mobile network operator testbed which emulates next generation networks, and enables researchers to design, implement and deploy future services and technologies. The testbed has been used broadly by different research institutions since it became operational back in May 2003.