The 107 type speaker ("Spokesman®") is designed to monitor the receiver leads of the handset. If the phone you are using will allow you to get inside and access the handset leads, then that is the way to do it. yes, you can power it from a 9-volt battery, but you will not get much time out of the battery. 18 Volts AC is the best way, applied to the yellow and black leads. Lower voltages will work, too.