local device = GsmModem.new('COM3', {
    baud         = '_9600';
    data_bits    = '_8';
    parity       = 'NONE';
    stop_bits    = '_1';
    flow_control = 'OFF';
    rts          = 'ON';
})
device:open(function(self, err, info)
  if err then
    print('Fail open port:', err)
    return self:close()
  end
  print('Connected to port:', info)
  -- Now we should configure modem to allow GsmModem class works properly
  -- (e.g. sms pdu mode, notify mode for sms and calls)
  -- Ofcourse you can use it as-is with out configure.
  self:configure(function(self, err, cmd)
    if err then
      print('Configure error:', err, ' Command:', cmd)
      return self:close()
    end
    print('Configure done')
    -------------------------------------------
    -- Here you can start do your work
    -------------------------------------------
  end)
end)

device:send_sms('+7777777', 'Hello world', function(self, err, ref)
  print('SMS Send result:', err or 'OK', 'Message reference:', ref or '<NONE>')
end)

device:send_sms('+7777777', 'Hello world', {waitReport = 'final'}, function(self, err, ref, response)
  if err or not response.success then
    print('SMS Send fail:', err or response.info, 'Message reference:', ref or '<NONE>')
  else
    print('SMS Send pass', 'Message reference:', ref or '<NONE>')
  end
end)

device:send_ussd('*100#', function(self, err, msg)
  print('USSD Result:', err, msg and msg:status(), msg and msg:text())
end)

device:on('sms::recv', function(self, event, sms)
  print("SMS from:", sms:number(), "Text:", sms:text())
end)

device:on('report::recv', function(self, event, sms)
  local success, status = sms:delivery_status()
  print("SMS reference:", sms:reference(), "Number:", sms:number(), "Success:", success, "Status:", status.info)
end)

-- read and delete first SMS from SIM card
device:read_sms(1, {memory = 'SM', delete = true}, function(self, err, sms)
  print("SMS from:", sms:number(), "Text:", sms:text())
end)

-- read all unreaded sms from phone memory
device:each_sms(GsmModem.REC_UNREAD, {memory='ME'}, function(self, err, idx, sms)
  if err and not index then
    -- e.g. invalid memory
    return print("List SMS error:", err)
  end

  if err then
    -- Some times device can return invalid sms on list (CMGL), but you can
    -- try read sms directly (CMGR) (e.g. device:read_sms(idx ...)
    -- This is works on my WaveCom SIM300
    return print("Read SMS #" .. idx .. " error:", err)
  end

  print("#" .. idx, "SMS from:", sms:number(), "Text:", sms:text())
end)