Avaya has made the mistake of allowing third party voice mail on Partner, Magix/Legend, and Definity. They will not make that mistake on IPOffice. As time goes on, you will see third party voice mail not work at all on Avaya's products.
It's more money for them. If you think I'm wrong, look at Nortel Networks. Try and put a third party voice mail on Norstar, BCM or Succession... It can be done, but the functionality that is lost is huge!
Neil
Ps. VoiceMail PRO is a very good product, I agree!