code: function CheckDevAckCB(err, results) {
          self.retry ++; // retry counter for ACK
          self.Debug (6, "CheckDevAckCB Phone=%s Retry=%d/%d Result=%j", smscmd.phone, self.retry, smsc.opts.retry, results);
          // ack no received
          if (results.length === 0) {
              if (self.retry <= smsc.opts.retry) {
                  setTimeout (function() {CheckDevAck ();}, smsc.opts.delay);
              } else {
                  self.Debug (7, "CheckDevAckCB Ack Abandoned MaxRetry=%s", smsc.opts.retry);
                  appcb ({status: -2, smsid: smscmd.id});
              }
          } else {
              // we may have more than one responses for a given command
              for (var slot in results) {
                  var ack =
                  { status: 2
                      , smsid: smscmd.id
                      , phone: smscmd.phone
                      , ack: results[slot].TextDecoded
                  };
                  // ACK received, delete it from inbox and send it to application
                  self.Debug (6, "CheckDevAckCB Ack Received %j", ack);
                  smsc.DelById (DelByIdCB, results[slot].Id);
                  appcb({status: 2, smsid: smscmd.id, msg: ack});
              }
              appcb({status: 0});
          }
      }
docs: this method is called by MySql when sms.GetFrom return