Emergency Call Centers (ECCs) have now to manage different streams of calls (vital emergencies, general medicine regulations…). To do so, ECCs use different workforce organizations based on dedicated or polyvalent skills on one hand, and based on different management rules for waiting queues of incoming calls. The purpose of this paper is to objectively study these different approaches in terms of waiting time and quality of service. Using a Discrete Event Simulation model, we demonstrated the clear benefits of merging queuing lines and developing multi-skilled human resources.