Can the HT814 support two lines per FXS port?


I have a POTS phone system with three lines where calls to the main number roll over to one of the other lines if the main line is busy (linear hunting group). All three lines are connected to an AT&T SynJ SB67138 which only has two RJ11 ports (lines 1 & 2 on one RJ11 port and lines 3 & 4 on the other).

Is it possible to configure the HT814 so that I can put two lines on one FXS port or would I have to get some kind of adapter to merge the two FXS port to the one jack on the SynJ?


The HT814 has ZERO FXO ports. Meaning, you can plug exactly ZERO lines from a phone company into it. It’s designed to plug phones into it. So the phones become extensions on a VoIP system.

What you need is a gateway device that will accept POTS lines and then turn those into SIP trunks for a PBX system to accept calls from (or send calls to).

An HT813 or HT503 each have one port on them, but this won’t be enough for you. If you need to plug in 3 POTS lines, you’ll need to consider higher end PBX gateway devices such as the UCM series (see and look for the 6204 4-FXO port model).

And I’ve never seen a VoIP gateway device outside of high end commercial modules that will support 4-wire duplexing like you’re talking about. Luckily, it’s almost trivially easy to split the two pairs into their own RJ11 connectors for just the cost of a foot of wire and two connectors, so maybe that’s why.


Whoops - I meant the GWX4104 4-port FXO gateway device.


Sorry, I didn’t make this clear in my initial post: I’m moving from this existing POTS to entirely VoIP, so I’m not looking to plug into an existing telephone company lines, just looking to use the existing POTS phone. In any case, I guess I’ll have to get some adapters to connect everything correctly.


Ah. The phone plugs into an FXS port, not FXO ports. FXS (Foreign eXchange Station) means “plugs into a device” and FXO (Foreign eXchange Office) means “plugs into a POTS line.” At one end of an analog connection is an FXO and at the other is an FXS. Meaning, the phone plugs into an FXS jack which eventually connects to an FXO port that the phone line plugs into.

If you want to plug analog phones into an HT814, that’s fine; you have 4 FXS ports so you can plug in up to 4 analog devices (phones, FAXes, whatever).

My confusion comes from when you switch and start talking about “lines.” Those are typically POTS analog wires that come out of the phone company’s central office, traverse dozens of miles of analog copper on a telephone pole, and then end at a jack on your wall that you then plug into your phone system or phone. THIS part, through the magic of two 2-pair wires in the jack, in a duplex arrangement. And it’s THIS part that I’ve never seen a VoIP FXO port handle as a duplex connection.

Again, you can take one duplex RJ11 connector, cut it off, split the pairs, and recrimp them on two separate RJ11 connectors if you need to split a duplex line. Assuming you have a duplex tool and some RJ11 connectors, it will take about 60 seconds.