[Linked Image from touchtonetommy.com]
This cat approves!

Viking Electronics made a "Micro Key" 1A2 around 1984 or so. 3 RJ-11's for the dial tone, Amphenols for the phones. Remove the ringer from the phone, remove the buzzer from the phone. Mount a 100-ohm speaker inside the housing, or use a spare U1 handset receiver element wired across the yellow/slate pair and another across the yellow/orange. Remove the locking key from the 4th pickup button. An audio generator spit out an obnoxious tone over the Y/S pair's speaker for ringing. Com on the 5th pickup button, go off hook and use the 4th pickup as a momentary button to open all of the other speakers on Y/O pair to make an all call announcement for someone to pickup the com line or a holding line. The only one I put in for my family's camera shop ran for 10+ years until putting in a Partner.