code: function(err, data) {
          var regexp = RegExp(/(Z\d)ON/);
          var ret;
  
          if (data) {
              for (i = 0; i < data.length; i++) {
                  if (ret = regexp.exec(data[i])) {
                      zones[ret[1]] = ret[1];
                  } else if (data[i] == 'PWON') {
                      zones['ZM'] = 'ZM';
                  }
              }
          }
          mdt.telnet('RR?', handleZoneNames);
      }
docs: get number of zones (PW? -> ["PWON","Z2ON","Z3ON"])