Going off some notes I have w/ my 616. You use extension 11.
The phone needs to have a LCD display.
The models I listed are
KX-T7020, KX-T7030, KX-T7050, KX-T7130, KX-T30830, KX-T30820, KX-T30850, KX-T61630, KX-T61620, KX-T61650.
I had copied this info from the manual when I was looking for a phone.
I think there may be some later models that would work as well.
I currently have my manuals packed away somewhere.
Jim