The increasing number of cellular users and the demand for broadband mobile communications (3rd and 4th generation) drives to the research of new methodologies for the design and evaluation of cellular networks and services. Simulation environments more than ever offer the opportunity to develop and study with low cost new structures and methods, including channel assignment schemes, for the implementation of new services. This paper thoroughly reviews centralized and distributed DCA schemes for GSM cellular systems in terms of simulation characteristics and needs and proposes a comprehensive simulation system incorporating their principles, entities and concepts involved. Moreover it proposes new efficient balanced DCA schemes minimizing cell congestion, leading to superior performance over rival assignment techniques. The proposed system is implemented in Java, in order to create a high performance generic simulation environment with the future capability of internetworking. The system is designed with the goal to be efficient in simulating large scale generic GSM cellular telecommunication systems in contrast to the majority of literature works where ad-hoc small cellular systems are presented. Moreover, another goal of the proposed system is to serve as a test bed for the evaluation and development of DCA schemes (especially for web based educational purposes) involved in such large scale cellular systems towards their planning as effective cellular mobile radio networks.