You CAN "manage" your messages through the web interface, but it doesn't play the messages through your computer, it calls you at an extension that you specify for the audio portion.

Unified Messaging requires an Exchange Server, and I believe it is only compatible with much older versions of Microsoft Exchange.

The programming GUI is pretty slick for building mass quantities of mailboxes on the initial installation, or fixing people's outcalling numbers without having to actually log into their mailboxes, but most simple changes are easier from the traditional DTMF interface.