In reply to a post by Pheasant:

Really only need the two centre pins to be present and cross-over.

If OP holds up each RJ11 plug side by side, very quick and easy to see if the colours transpose at either plug.

Not necessarily, reversing pins 3 and 4 may well not make any difference. I even have a BT phone which has a switch on the bottom which does just that so that some indicator light works.

The OP's phone quite possibly comes with a cable with and RJ11 on one end and a BT 431A plug on the other. The phone might use pins 3 and 4 or 2 and 5. So long as the cable is compatible it won't matter.

Thanks to both of you!

I put all the cables in front of me.

Two of them was an old VDSL2 modem cable - 2 centre pins (no crossover)
One of them was pins 2,3,4,5 - run straight through (no crossover)

....then I rechecked the cable with the BT plug at the end and each cable crossed over.

I ordered the cable you recommended me and that should turn up Monday, these are very old phones so maybe that's the issue, at least I know what's going on now.

Edited by juzzy25 (Wed 24-Nov-21 23:14:26)

As per post above, now that the gallery photos work, its quite clear the OP's phone have pins 2 & 5 wired in the RJ11 - his FXS port will be wired for the centre pins 3 & 4.

So OP needs a double crossover cable RJ11 male to RJ11 male wired 2->3, 3->2, 4->5, 5->4

Well good luck. I hope I am right. I have had the same problem with other equipment.

Where do I get that cable from then?

It's a tough one to Google.

https://www.leadsdirect.co.uk/shop/rj11-telecomms-do...

So what are 2 and 3 on one end connected to on the other end?

The 'A' end and the 'B' end of the cable are reversible.

Basically the OP as I think I understand it, has handsets which use position 2 and 5 on the RJ11 (the outside pins). The FXS port on the ATA would typically use positions 3 and 4 (the centre pins).

Therefore ti get a connection, we need to get position 2 on the handset port to position 3 on the FXS port and likewise postion 5 on the handset port to position 4 on the FXS port.

The unused pin/pairs aren't needed but as said allow the cable to be reversed/plugged in either way.

Its easier if you draw a picture/trace out the pinout.

Like this:

https://postimg.cc/1fcw5Jkb

Admittedly much faster/easier with a bag of RJ11 plugs and a crimp tool in the toolbag to make your own leads up.

That is what I think but I don't think the product description on the web site is much good as one could read it as 2 and 3 on one end going to 3 and 2 on the other end, and 4 and 5 going to 5 and 4.