The hookswitches in many 1A2 phones have more contacts then are needed for the phone to work. For example, some designs interrupt both the tip-side and ring-side of the phone line. One is enough for normal phone operation.
Check the schematic and connect the contacts of a spare switch to a spare wire pair. Use the switch closure to activate a relay (you'll need a power source, too) to disconenct the speakers in a TV or stereo system when the handset is picked up.