I have found rather often that I need to set the permissions on a mailbox, but the language may not be in English. This is especially true for Calendars. I used this script when setting up Polycom Real Connect. You would want to change the filter and the user attributes
a few things, you may want to user a better filter for the displayname for just your conference rooms, you could do a filter on roomtype
Now you may have forgotten the account you want to use for the UPNofUser, you can do that by just getting the information of an existing mailbox.