Abstract: An extension-in-use exclusion apparatus is for use in a telephone system. The system has a telephone device, a telephone line, and two telephone extensions connected to the line. The apparatus is connected between one extension and the telephone device. The apparatus has an exclusion controller connecting the line to the telephone device when all extensions other than the extension for the telephone device are on-hook and the telephone device extension is off-hook. The exclusion controller does not connect the line to the telephone device when another extension is off-hook and the telephone device is off-hook. A user operable switch can instruct the exclusion controller to connect the line to the telephone device when another extension is off-hook and the telephone device is off-hook. The apparatus automatically returns to exclusion mode when the telephone device returns to off-hook. A by-pass allows FSK signals to pass directly through to the telephone device.

Abstract: A device that links a telecommunication device (for example a data terminal, a telephone instrument, a message terminal or a video terminal) directly to a telephone line for cancellation of a call waiting tone. When an incoming call is received by the linked telecommunication device, the device according to the invention places the interface terminal on hold while maintaining it on line, while a special call waiting cancellation DTMF code such as "*70" is generated and transmitted. Following this action, telecommunication device is returned to the line and the original transmission is allowed to resume.