AT&T used to sell A Voice mail called a classic mail. I was also called a Voysys.

First off if you get one itwill be close to 10 years old.
Second it uses 4 of yout extention ports (one of which is 10)
Third It is acient technology. They Barely integrate with the merlin and I would not sell one to any on my customers (even ones I don't like I want to get rid of)

You would be much better off selling them A Partner, Vodavi STS, or an NEC DS2000 or any other system you sell