Although no specific support documentation on the 3CX site, the MP104 seems to be compatible and recommended as far as I'm concerned. Choose the MP114 option during gateway set-up. The port quantity selection was a bit squirrely, but made it through. Unit registers fine and seems to be working bug free. I'm only using one port for PSTN access through pots line, but works great for 911, local calls, or as an alternate route.