How many lines do you need? Also many major cell phone companies sell land line boxes you can just plug the RJ11 output into each PBX CO port and buy more of these land line simulator boxes. To be clear these boxes were designed for residential but there is no reason you could not buy multiple boxes for as many CO (Central Office) lines you want on your PBX. Also there are very few PBXs now and most are KSU and all are dying out to voice over IP systems.