"The present document specifies the stage one description of the Voice Group Call Service (VGCS) which allows speech conversation of a predefined group of service subscribers in half duplex mode on the radio link taking into account multiple mobile service subscribers involved in the VGCS call per cell. The VGCS is applicable to all mobile stations in a certain network and area which have the technical capability and the corresponding subscription@ respectively@ to participate in a VGCS call. NOTE: It is not considered as requirement that normal GSM phase 2 mobile stations will be able to be used for this service. The service is described from the service subscriber""s and user""s point of view; in particular: - the procedure for normal operation with successful outcome; - the action to be taken in exceptional circumstances; - the interaction with other GSM services and features. The present document does not deal with the Man-Machine Interface (MMI) requirements@ but makes reference to the appropriate Global System for Mobile Communications (GSM) specifications. The present document defines a teleservice of the digital cellular telecommunications system GSM. Any interaction with other services and/or networks not dealt with in clauses 7 or 8 are outside the scope of the present document."