A shy try to see how important Queuing theory and what a significant role it can play in improving the quality of services in our life, As the global call center industry continues to grow, Starting by reviewing the process in the call centers, Knowing its characteristics, and how do we evaluate the service level, Also how it shows the call centers depend on this field in order to optimize their services and gain the client satisfaction; In addition to the way they handle the incoming calls. Also this study slightly focus on how Erlang models work in the call centers.