Abstract: A voice over internet method and system is disclosed to enable radio devices to initiate or terminate a session initiation protocol for transmission of audio data over the internet. A gateway (12) is provided which includes a processor (50) and a software layer (70) to enable signals other than conventional off-hook and on-hook signals to initiate a session. The processor (50) and software (70) detect a control signal which includes data to identify the signal as a request to initiate or terminate a session. The control signal may have a control tone followed by at least one signal tone followed by one further control tone. The control tones represent the data identifying the signal as a request to initiate or terminate a session, and the signal tone identifies the end destination of the call.