Grandstream HT802 Integration - busy tone?

Still new to HA and adding things as I find them. Today, I am trying to use my Grandstream HT802 and set it up for phone integration as described here.
When I pick up the line, I get a busy tone.
Things I have tried:

  • Added an autopickup delay in the HT802 settings. Then I get a dial tone and after the timeout it switches to busy.
  • Switched around the Vocoder preferences so that OPUS is in first place. Payload type is correct.
  • Added SIP user 37 to the Voip integration settings in HA, to match the direct dial setting in the HT801
  • Switched to different port settings on both ends
  • Nothing relevant in the HA logs

What else do I have:

  • HA 2025.3.3
  • HT802 is configured with both lines registered with separate phone numbers at voip.ms.
  • One of the numbers I don’t use and can repurpose for HA. This is the one on line 2.

Do I not understand the capabilities of this integration? I assumed that I will be able to call my number from outside and talk to HA, but I suspect this may not work if the HT802 is registered on a VOIP server. Did I miss something else?

After re-reading the documentation, I have to answer this myself. The intent of the integration, and the capabilities of the MT802, clearly limit it to controlling the HA from a phone that is plugged into the adapter. A SIP call to the same port will never trigger the Offhook auto-dial. Sad, because I can’t think of a useful scenario for this.
With that limitation, I still could not get it to work. I swapped the lines and ports so that port 1 would be the one that’s auto-dialing to HA, still only a busy signal. When I remove the auto dial setting, the line and port work normally, i.e. I get a dial tone and can make an outbound phone call. I also tried with the line not registered at the sip server, same busy signal.

Is the POT (Plain Old Telephone) plugged directly into the RJ-11 or is it on the household telephone wiring?

Have you tried a different telephone? (A really old one).

I have not tried a really old phone. I used a Panasonic cordless phone, from the base station, plugged into the MT802.

The older phones detect ‘off-hook’ by a small current passing through the wires back to the central office. Try putting a 1K resistor across the red-green pair from the phone.

I have an older phone somewhere in the attic, will look for it eventually. I have moved on from this for now.