A conference call facility is described in which one (2a) of a group of communication devices (2a,2b,2c,2d) connected to a low power radio frequency network (9) is able to set up a call to a party external of the network (9) and then selectively add further devices (2a,2b,2c) to the call under the control of the user of the one device (2a). The users of the other devices (2b,2c) are able to enable or disable the selection of their device in a conference call. One or more of the communication devices may be a mobile radio telephone equipped with the necessary network interface (1).