As the usage of Internet extends rapidly nowadays an increasing variety of communication forms can be observed. It is practical to handle all the existing and evolving forms of communication uniformly. IMS offers such a solution for this based on IP protocol. Due to its control structure IMS provides a flexible possibility to deploy new services. Group messaging is one of the above mentioned forms. Users would like to share information with their contacts in a fast, simple way by using integrated services with additional values. Such additional function could be the possibility of sending any kind of multimedia message instead of just text message. In this thesis I examine the criteria of group messaging services, discuss potential solutions with their pros and cons. I implement the service and client application with the most suitable method in Java, and test whether it corresponds to the specifications. At the end I collect development opportunities which could improve future usability.