The deployment of mobile telecommunication networks for the new UMTS standard poses new challenges for radio network planning. In contrast to, for example, GSM, coverage and capacity cannot be considered separately. There are simulation tools for network engineers, but the quality of these tools remains to be shown. Methods and tools for systematic optimization of base station configurations in their complex interaction are just emerging. The European project MOMENTUM, an acronym for Models and Simulations for Network Planning and Control of UMTS, aims at this. Techniques and algorithms for planning and optimizing the UMTS radio interface are being developed, which shall eventually be used in operators' planning and optimization tools. According to this goal, besides research groups from mathematics and telecommunications the consortium consists of a manufacturer and three operators.