Vertical makes the Interchange voice mail, which is the Windows based OS that does what the old DOS keyvoice systems did. It is not the cheapest system out there, but it is very solid and can do almost anything that a customer would want (in reason). I am not 100% on the integration with Avaya though, but I have them on Siemens and Tadiran systems (and of course Vertical FXII systems).

Steve