According to the documentation I have from AVAYA, the 6402D is NOT a supported set. The smallest of the 6400 series sets would be the 6408D.
You have to remember, all 6400 series sets are based on the same hardware and software, so you *may* get some functionality out of the 6402D, but AVAYA has not created the IPOffice operating software to work with the 6402D.
Neil