Developing Short Message Service (SMS) and Enhanced Message Service (EMS)services require advanced and complex testing to assure the reliability, durability and credibility of the services. Such tests include various error scenarios within the Global System of Mobile communications (GSM) networks, i.e. packet loss and bit errors. In any arbitrary GSM networks such errors rarely appear and are almost impossible to repeat, which makes test results quite unreliable. This master thesis presents a simulation of a Short Message Service Centre (SMSC). A SMSC is the part of a GSM network that handles the messaging, e.g. SMS and EMS transmissions. By placing the SMSC in a Transport Control Protocol/Internet Protocol (TCP/IP) environment both money and time are saved, through the reliability and speed of modern Local Area Networks (LAN). The implementation of the SMSC Simulator (SMSCS) proved to be very satisfying. It was very well received by the developers, as an eagerly awaited complement for the SMS and EMS service development. Almost any kind of error scenario can be generated through the simulator, since it allows both data manipulation and traffic generation.