The simple answer is yes. You create Mailboxes, by going to Dashboard > My VoIP > Config > Mailboxes. From here you can create mailboxes and configure everything about them; do you want to receive email notifications, if so to which email address, would you like a custom greeting etc.
Once you've created your mailbox you then chose how you would like to use it. You can either assign it to a SIP User (A person) by going to Dashboard > My VoIP > Users and make it their personal voicemail that gets played if they don't answer their extension number, or you can assign it to any part of a Call Route that you wish.
You set up call routes under Dashboard > My VoIP > Routing > Call Routes. A Call Route would do something like dial a user or group of users for say 30 seconds and then go to your "we are very busy" Mailbox if non responsive. "Call Routes" are a little like mailboxes, you can create and save as many of them as you want, but you must then go and use them by attaching them to a number under Dashboard > My VoIP > Numbers or using them in an Out of Hours diary. That way when you call say 0207 111 1234 you are telling that number to follow X call route which in turn finish's with X mailbox.