A device for processing a signaling message related to a communication service provided to a client device via a communication network. When the client device is connected via an access network operating in circuit mode, the device translates a first signaling message for the circuit mode into a second signaling message suitable for being carried over the access network operating in packet mode, and vice versa. When the client device is connected via the access network operating in packet mode, the processing device receives from the client device a third signaling message suitable for being carried over the access network operating in packet mode and sends the third signaling message to a server of the communication network subsystem, and vice versa, and replaces in the received third signaling message a source address, including an address of the client device, with an address of the processing device.