TOA Telephone/PA system interface
	Approved by BT for use with commercial phone systems which employ inphone type sockets Allows system users to make direct announcements over an Eagle public address system An extension number is allocated and a BT5 interface is connected in lieu of an extension phone: any call received will be acknowledged by a tone, after which the caller may speak. The BT5 will give engaged signals to other callers when in use and will automatically reset when the caller has stopped speaking Suitable only for 2-wire phone systems