Radio communications gateway device for retransmitting messages of different forms between a first radio communications network and a second radio communications network, said gateway device (200, 300) comprising: - a first transmitter capable of processing the radio communications of the first network according to a first coding scheme, - a second transmitter capable of processing the radio communications of the second network according to a second coding scheme, and - a switch which, when the gateway device is activated, connects the first and second transmitters (214, 216) in order to retransmit voice messages from a group communication processed by one of said transmitters (214, 216) to the other of said transmitters (214, 216), characterised in that it comprises: • a controller for automatically implementing: - the gateway device in active mode upon reception of a voice message of a group communication by analysis of signalling messages of said voice messages indicating a group communication; - the gateway device in suspended mode by automatically suspending the switch so that said first and second transmitters (214, 216) process independently of one another messages received between the gateway device and respectively one of the two radio communication networks, the suspended mode being activated when signalling data of the messages received by one of the transmitters does not indicate group voice communication. • at least one man-machine interface connected to the transmitters and comprising communication configurations dedicated to the processing of each transmitter, in such a way that a user of the gateway device can communicate with at least one terminal of one of the two radio communications networks (202, 204) when the suspended mode is activated. - a first transmitter capable of processing the radio communications of the first network according to a first coding scheme, - a second transmitter capable of processing the radio communications of the second network according to a second coding scheme, and - a switch which, when the gateway device is activated, connects the first and second transmitters (214, 216) in order to retransmit voice messages from a group communication processed by one of said transmitters (214, 216) to the other of said transmitters (214, 216), characterised in that it comprises: • a controller for automatically implementing: - the gateway device in active mode upon reception of a voice message of a group communication by analysis of signalling messages of said voice messages indicating a group communication; - the gateway device in suspended mode by automatically suspending the switch so that said first and second transmitters (214, 216) process independently of one another messages received between the gateway device and respectively one of the two radio communication networks, the suspended mode being activated when signalling data of the messages received by one of the transmitters does not indicate group voice communication. • at least one man-machine interface connected to the transmitters and comprising communication configurations dedicated to the processing of each transmitter, in such a way that a user of the gateway device can communicate with at least one terminal of one of the two radio communications networks (202, 204) when the suspended mode is activated. • a controller for automatically implementing: - the gateway device in active mode upon reception of a voice message of a group communication by analysis of signalling messages of said voice messages indicating a group communication; - the gateway device in suspended mode by automatically suspending the switch so that said first and second transmitters (214, 216) process independently of one another messages received between the gateway device and respectively one of the two radio communication networks, the suspended mode being activated when signalling data of the messages received by one of the transmitters does not indicate group voice communication. - the gateway device in active mode upon reception of a voice message of a group communication by analysis of signalling messages of said voice messages indicating a group communication; - the gateway device in suspended mode by automatically suspending the switch so that said first and second transmitters (214, 216) process independently of one another messages received between the gateway device and respectively one of the two radio communication networks, the suspended mode being activated when signalling data of the messages received by one of the transmitters does not indicate group voice communication. • at least one man-machine interface connected to the transmitters and comprising communication configurations dedicated to the processing of each transmitter, in such a way that a user of the gateway device can communicate with at least one terminal of one of the two radio communications networks (202, 204) when the suspended mode is activated.