Panasonic 616 polarity reverse on payphones.

[dsk]

Hi
My payphones is made for polarity change when party answers. I want to use them on the lines on my 616.
The polarity change is only needed when the trunk line party answers.

Is it a simpler solution than this (Chematics) when the trunkline changes the polarity a relay will switch the polarity on 2 lines on the 616?