A user device comprising: a network interface for connecting to a network; an audio output component for outputting audio signals; a processor configured to execute a communication client, said client operable to: join a conference call conducted over said network; at the user device, code an identifier into audio generated at the user device; and during the call, output said audio via the audio output component such that said audio can be received and processed to identify the user device by another user device, in the vicinity of the user device, already participating in the call; characterised in that the client is further operable to: receive a notification from the other user device via the network; determine, based on the received notification, that the other user device has identified the user device and responsive to said determination, to do at least one of: notify a user of the user device of said identification via a user interface of the client; reduce an audio level at the user device; supply audio from an audio input component of the user device to an audio processing component for processing; trigger selection by a selection component of one of an audio input component of the user device and an audio input component of the other user device for use during the call. a network interface for connecting to a network; an audio output component for outputting audio signals; a processor configured to execute a communication client, said client operable to: join a conference call conducted over said network; at the user device, code an identifier into audio generated at the user device; and during the call, output said audio via the audio output component such that said audio can be received and processed to identify the user device by another user device, in the vicinity of the user device, already participating in the call; characterised in that the client is further operable to: receive a notification from the other user device via the network; determine, based on the received notification, that the other user device has identified the user device and responsive to said determination, to do at least one of: notify a user of the user device of said identification via a user interface of the client; reduce an audio level at the user device; supply audio from an audio input component of the user device to an audio processing component for processing; trigger selection by a selection component of one of an audio input component of the user device and an audio input component of the other user device for use during the call. join a conference call conducted over said network; at the user device, code an identifier into audio generated at the user device; and during the call, output said audio via the audio output component such that said audio can be received and processed to identify the user device by another user device, in the vicinity of the user device, already participating in the call; characterised in that the client is further operable to: receive a notification from the other user device via the network; determine, based on the received notification, that the other user device has identified the user device and responsive to said determination, to do at least one of: notify a user of the user device of said identification via a user interface of the client; reduce an audio level at the user device; supply audio from an audio input component of the user device to an audio processing component for processing; trigger selection by a selection component of one of an audio input component of the user device and an audio input component of the other user device for use during the call. receive a notification from the other user device via the network; determine, based on the received notification, that the other user device has identified the user device and responsive to said determination, to do at least one of: notify a user of the user device of said identification via a user interface of the client; reduce an audio level at the user device; supply audio from an audio input component of the user device to an audio processing component for processing; trigger selection by a selection component of one of an audio input component of the user device and an audio input component of the other user device for use during the call. notify a user of the user device of said identification via a user interface of the client; reduce an audio level at the user device; supply audio from an audio input component of the user device to an audio processing component for processing; trigger selection by a selection component of one of an audio input component of the user device and an audio input component of the other user device for use during the call.