I have 2 avaya partner phone systems with the phone off the 110 hooked to the 6th line port and an analog station off the partner hooked to the 110s line port. They can call the phones on the other phone system no problem, doing 2 13 # to get to extension 13, but to voice over they have to they have to 2 *13 # and that doesn't work. They really like to voice over because the engineers in the other building just ignore them if they can only ring there.