The solution is very simple. It works for our Wantec Monolith IP here.
The Wantec can only call/send http, that is like entering the lines to the browser. So you can test it using the browser instead of walking to the door and push the button.
If you use Openhab 1 then the Wantec entry is:
http://192.168.178.20:8080/CMD?Tor_Klingel=ON
If you use Openhab 2:
http://host:port/classicui/CMD?itemName=command
(Classic UI installation required)
This is the host and port of the device OH is running on.
The BasicUI should provide the servlet, too, but I don’t know the path.
But please don’t forget that openhab was NOT made to use it in this way. This is not an official feature.
You should define an item accordingly before.
The Wantec Monolith IP Phone cannot send or use any of the programs PHP, curl, wget from the line offered by the browser UI…
Another possibility to bring the Wantec to openhab is using one of the relays. But you would have to buy some hardware to read out the relays and some more cable to the door.
(Would be great if you could post your solution also to the KNX user forum)