A first terminal is coupled to a wide-area packet-based network and installed with first client application. One or more second terminals are coupled to the first terminal via a local wireless link, and each installed with an instance of a lightweight sub-client having reduced functionality relative to the first client. The first client establishes a call with a remote, third terminal over the network, based on a user credential identifying the first client. Each second terminal generates an audio or video stream, and each sub-client transmits the respective stream to the first client over the local wireless link for use in the call. The first client switches between a second state in which the call uses the streams from the sub-clients and a first state in which the call uses a stream generated by the first terminal without the streams from the sub-clients.