There is described a gateway system comprising: a local-call device for receiving and sending phone call signals from and to a telephone device located in a same telecommunication zone; a VoIP device, distinct from the local-call device, for receiving and sending VoIP call signals from and to a remote and distinct VoIP device located in another distinct telecommunication zone; and a voice transmission apparatus comprises a set of two acoustically distinct chambers. Those comprise a first chamber comprising a first microphone and a second speaker; and a second chamber comprising a second microphone and a first speaker. The first microphone and the first speaker are in communication with the local-call device only and the second microphone and the second speaker are in communication with the VoIP device of the gateway system only.