Maintenance of group call in mobile communication system

A method of maintaining a group call in a mobile communication system comprising a network infrastructure and mobile stations, the method comprising the steps of: establishing a group call in which a first mobile station is prioritized and the mobile stations participating in said group call communicate in speech items, the frame structure comprising time slots that a second mobile station sending a speech item employs in its speech item. In the method, the first mobile station is allocated time slots or time periods in which only the first mobile station can transmit signalling messages to the network infrastructure; the first mobile station and the third mobile stations are transmitted data indicating in which time slots of time periods only the first mobile station can send signalling messages to the network infrastructure; and the third mobile stations refrain from sending their signalling messages in the time slots or time periods allocated to the first mobile station.