The invention relates to a mobile communication system including mobile stations comprising transmission means for sending data over the radio path, at least one mobile exchange, and base stations having a data transmission connection with the mobile exchange, traffic channels being allocated to be used by transceiver units of the base stations for providing calls to the mobile stations, the base stations also comprising means for receiving the data sent by the mobile stations over the radio path and for forwarding said data to other parts of the system. In order for the mobile stations to be able to send data more efficiently, at least one predetermined data channel is allocated for the mobile stations to send data. In addition the system includes at least one mobile station comprising control means that independently at predetermined moments control the transmission means of the mobile station to move over to said predetermined data channel for the time the data is sent, in which case the mobile station sends said data on said data channel without a preceding channel allocation.