Requirements and status analysis of the telecommunication market have been carried out in this thesis, in order to implement a new generation of mobile telecommunication system. The requirements for implementation of Universal Mobile Telecommunication System (UMTS) have been explored, processed and specified, applying requirements engineering and use cases from the access, core network and control layer point of view. It has been proven that requirements engineering is applicable in telecommunications for a systematic process of requirements specification by an iterative interactive process of problem analysis, solution development and their verification. A model of telecommunication network with UMTS has been developed. The model is described by means of use cases. High level use cases, which are most relevant for the implementation of UMTS, are presented. Possible scenarios for the migration from a GSM network to an UMTS network have been elaborated. Two case studies for the implementation of UMTS have been made; one for network operator with an existing GSM network and another for an UMTS network operator only. Solutions for specified requirements have been proposed. A scenario evaluation has been performed on a national mobile telecommunication network of an average-sized European country. Relevance of the models and scenarios has been proven in the case of migration from the second to the third generation telecommunication system within a dedicated time-plan and predicted traffic data.