Abstract: In a communication system, a plurality of subscriber identity modules implemented as cards and to be mounted to mobile stations (MSs) share a single international mobile subscriber identity (IMSI). When any one of the MSs generates an authentication and registration request, a mobile services switching center (MSC) at a home station writes information representative of the combination of the identity IMSI and an international mobile equipment identity IMEI attached to the mobile station in a home location register. When any one of the MSs generates a call origination request or when a call termination request meant for any one of them is generated, the MSC at a home station or an MSC at a roamer station provides the requested service only if combination information relating to the mobile station is stored in the home location register or a visitor location register.

Abstract: A speech control circuit is disclosed for use in a loudspeaker telephone or a handsfree telephone having a microphone and a speaker, and provides the correct switching of the transmission mode and the reception mode in spite of acoustic coupling between the speaker and the microphone. The disclosed circuit reduces errors in the switching operation and helps to prevent the problem of "noise block".

Abstract: In a voice control circuit comprising a variable loss circuit and a voice level detector which is connected to control the variable loss circuit, there is provided a noise control circuit. The noise control circuit comprises a timer which discriminates as noise an input having a constant amplitude and persisting for greater than a greater than a predetermined interval, a noise level detector and a variable attenuator connected on the input side of the voice level detector and which functions to attenuate the voice signal in accordance with the detected level of the noise.