code: def get_user_availability(email_address, start_time, end_time)
        opts = {
          mailbox_data: [ :email =>{:address => email_address} ],
          free_busy_view_options: {
          time_window: {start_time: start_time, end_time: end_time},
        }
        }
        resp = (Viewpoint::EWS::EWS.instance).ews.get_user_availability(opts)
        if(resp.status == 'Success')
          return resp.items
        else
          raise EwsError, "GetUserAvailability produced an error: #{resp.code}: #{resp.message}"
        end
      end
docs: Get information about when the user with the given email address is available.
   @param [String] email_address The email address of the person to find availability for.
   @param [DateTime] start_time The start of the time range to check as an xs:dateTime.
   @param [DateTime] end_time The end of the time range to check as an xs:dateTime.
   @see http://msdn.microsoft.com/en-us/library/aa563800(v=exchg.140)