We propose a novel interference management framework for the cellular downlink through cooperative transmission. A sectored cellular network is studied where the interference is only due to sectors in neighboring cells and intra cell interference is ignored. We first explore the potential degrees of freedom (DoF) gain in a scenario where mobile receivers can be associated to any neighboring cell but no cooperative transmission is allowed. We show that the maximum achievable per user DoF for orthogonal schemes is between 1/3 and 3/7. On the other hand, if cooperative transmission is combined with flexible message assignment to the transmitters, we show that it is possible to achieve a per user DoF of 7/15. In addition, the proposed cooperative transmission scheme does not require extra backhaul capacity, as it uses a smart assignment of messages to transmitters to meet an average backhaul load constraint of one message per transmitter.