I thought this was pretty cool, so I wanted to share. This last week, I onboarded a client who had an old analog phone system that was integrated into a PA system around their shop and warehouse. When they pressed the intercom button on their phones, it sent an intercom to the speakerphone output of all their phones as well as an RCA jack plugged into the PA amplifier. In order to keep that functionality with the new VoIP 3CX phone system, I created a page group that included all the new VoIP phones and I put a custom speed dial on each phone labeled "Intercom" which dialed that page group. Although this worked to send an intercom message to each phone, I still needed to integrate the old PA system with the audio sent over the intercom speed dial. To do that, I used a dedicated Yealink T42G which by default sends all audio (including page audio) through its headset connection when headset output is enabled. I connected an RJ9 to 3.5mm adapter to the headset connection on the T42G and then I used a 3.5mm to RCA adapter and then I added the T42G to the page all group so when someone presses the "Intercom" speed dial on their new VoIP phone, all the VoIP phones send the intercom audio through their speakerphone as well as the T42G which send the intercom audio out of its headset connection and through the PA system. Although this is a "quick-and-dirty" fix I feel that it is stable enough to keep as a permanent solution for having audio from 3CX go through an existing intercom system.