The current user import CSV only lists five supported fields (First Name, Last Name, Email, User Role, and Password). However, I know more fields are supported. They're just not shown in the CSV example. Other supported fields are Fax Caller ID, Password (TRUE/FALSE), Fax CSID, Fax (TRUE/FALSE), and Drive (TRUE/FALSE). I would love to see a more robust user import CSR that at least supports uploading all fields under a user's fax tab.