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Send and Read SMS through a GSM Modem using AT Commands

, 30 Aug 2010 CPOL
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In this article, you can send and read SMS through a GSM modem using AT commands and without using any third party library.


There are many different kinds of applications SMS applications in the market today, and many others are being developed. Applications in which SMS messaging can be utilized are virtually unlimited. Some common examples of these are given below:

  • Person-to-person text messaging is the most commonly used SMS application, and it is what the SMS technology was originally designed for.
  • Many content providers make use of SMS text messages to send information such as news, weather report, and financial data to their subscribers.
  • SMS messages can carry binary data, and so SMS can be used as the transport medium of wireless downloads. Objects such as ringtones, wallpapers, pictures, and operator logos can be encoded in SMS messages.
  • SMS is a very suitable technology for delivering alerts and notifications of important events.
  • SMS messaging can be used as a marketing tool.

In general, there are two ways to send SMS messages from a computer / PC to a mobile phone:

  1. Connect a mobile phone or GSM/GPRS modem to a computer / PC. Then use the computer / PC and AT commands to instruct the mobile phone or GSM/GPRS modem to send SMS messages.
  2. Connect the computer / PC to the SMS center (SMSC) or SMS gateway of a wireless carrier or SMS service provider. Then send SMS messages using a protocol / interface supported by the SMSC or SMS gateway.

In this article, I will explain the first way to send, read, and delete SMS using AT commands. But before starting, I would like to explain a little bit about AT commands.

AT Commands

AT commands are instructions used to control a modem. AT is the abbreviation of ATtention. Every command line starts with "AT" or "at". That's why modem commands are called AT commands. There are two types of AT commands:

  1. Basic commands are AT commands that do not start with a "+". For example, D (Dial), A (Answer), H (Hook control), and O (Return to online data state) are the basic commands.
  2. Extended commands are AT commands that start with a "+". All GSM AT commands are extended commands. For example, +CMGS (Send SMS message), +CMGL (List SMS messages), and +CMGR (Read SMS messages) are extended commands.

If you want to get more information about AT commands, then you can get it on my other article on CodeProject here:

Operating Modes

The SMS specification has defined two modes in which a GSM/GPRS modem or mobile phone can operate. They are called SMS text mode and SMS PDU mode. (PDU stands for Protocol Data Unit.) The mode that a GSM/GPRS modem or mobile phone is operating in determines the syntax of some SMS AT commands and the format of the responses returned after execution.

I am using SMS text mode in this article.

How to Test GSM Modem Connectivity Using Hyper Terminal

  • First, find the best GSM modem that suits the needs. I tested this application with a Wavecom FASTRACK M1206.
  • Understand the AT Command set required to communicate with the modem.
  • Connect the modem to the computer according to the setup guide specified in the manual provided with the GSM modem.
  • Put a valid SIM card into the mobile phone or GSM/GPRS modem.
  • Connect your mobile phone or GSM/GPRS modem to a computer, and set up the corresponding wireless modem driver.
  • Run the MS HyperTerminal by selecting Start -> Programs -> Accessories -> Communications -> HyperTerminal.
  • In the Connection Description dialog box, enter a name and choose an icon you like for the connection. Then click the OK button.
  • In the Connect To dialog box, choose the COM port that your mobile phone or GSM/GPRS modem is connecting to in the Connect using combo box. For example, choose COM1 if your mobile phone or GSM/GPRS modem is connecting to the COM1 port. Then click the OK button.
  • The Properties dialog box comes out. Enter the correct port settings for your mobile phone or GSM/GPRS modem. Then click the OK button.
  • To find the correct port settings that should be used with your mobile phone or GSM/GPRS modem, consult the manual of your mobile phone or GSM/GPRS modem.
  • Type "AT" in the main window. A response "OK" should be returned from the mobile phone or GSM/GPRS modem.
  • If “OK” returns, it means your mobile phone or GSM/GPRS modem is connected successfully.

After successful connection of the GSM /GPRS modem with PC, you are ready to run this application. Download the attached project and run the application.

Sending SMS through GSM Modem using AT Commands

Port Settings

In this tab, you will have to do port settings which will be the same as you did in the hyper terminal and then click the OK button. If the modem is connected successfully, a message box will appear with the message “Modem is connected”.

public SerialPort OpenPort(string p_strPortName,
       int p_uBaudRate, int p_uDataBits, 
       int p_uReadTimeout, int p_uWriteTimeout)
    receiveNow = new AutoResetEvent(false);
    SerialPort port = new SerialPort();

        port.PortName = p_strPortName;                 //COM1
        port.BaudRate = p_uBaudRate;                   //9600
        port.DataBits = p_uDataBits;                   //8
        port.StopBits = StopBits.One;                  //1
        port.Parity = Parity.None;                     //None
        port.ReadTimeout = p_uReadTimeout;             //300
        port.WriteTimeout = p_uWriteTimeout;           //300
        port.Encoding = Encoding.GetEncoding("iso-8859-1");
        port.DataReceived += new SerialDataReceivedEventHandler
        port.DtrEnable = true;
        port.RtsEnable = true;
    catch (Exception ex)
        throw ex;
    return port;

Send SMS

In the second tab, you can send SMS:

public bool sendMsg(SerialPort port, string PhoneNo, string Message)
    bool isSend = false;

        string recievedData = ExecCommand(port,"AT", 300, "No phone connected");
        recievedData = ExecCommand(port,"AT+CMGF=1", 300,
            "Failed to set message format.");
        String command = "AT+CMGS=\"" + PhoneNo + "\"";
        recievedData = ExecCommand(port,command, 300,
            "Failed to accept phoneNo");
        command = Message + char.ConvertFromUtf32(26) + "\r";
        recievedData = ExecCommand(port,command, 3000,
            "Failed to send message"); //3 seconds
        if (recievedData.EndsWith("\r\nOK\r\n"))
            isSend = true;
        else if (recievedData.Contains("ERROR"))
            isSend = false;
        return isSend;
    catch (Exception ex)
        throw new Exception(ex.Message);

Read SMS

In the third tab, you can read SMS:

public ShortMessageCollection ReadSMS(SerialPort port)
    // Set up the phone and read the messages
    ShortMessageCollection messages = null;
        #region Execute Command
        // Check connection
        ExecCommand(port,"AT", 300, "No phone connected");
        // Use message format "Text mode"
        ExecCommand(port,"AT+CMGF=1", 300, "Failed to set message format.");
        // Use character set "PCCP437"
        ExecCommand(port,"AT+CSCS=\"PCCP437\"", 300,
        "Failed to set character set.");
        // Select SIM storage
        ExecCommand(port,"AT+CPMS=\"SM\"", 300,
        "Failed to select message storage.");
        // Read the messages
        string input = ExecCommand(port,"AT+CMGL=\"ALL\"", 5000,
            "Failed to read the messages.");

        #region Parse messages
        messages = ParseMessages(input);
    catch (Exception ex)
        throw new Exception(ex.Message);

    if (messages != null)
        return messages;
        return null;

Delete SMS

In the fourth and last tab, you can count the number of SMS and delete SMS as well.

public bool DeleteMsg(SerialPort port , string p_strCommand)
    bool isDeleted = false;
        #region Execute Command
        string recievedData = ExecCommand(port,"AT", 300, "No phone connected");
        recievedData = ExecCommand(port,"AT+CMGF=1", 300,
            "Failed to set message format.");
        String command = p_strCommand;
        recievedData = ExecCommand(port,command, 300, "Failed to delete message");

        if (recievedData.EndsWith("\r\nOK\r\n"))
            isDeleted = true;
        if (recievedData.Contains("ERROR"))
            isDeleted = false;
        return isDeleted;
    catch (Exception ex)
        throw new Exception(ex.Message);

Points of Interest

I'm not using any third party library or anything else in this project.


  • 4th August, 2009: Initial post.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Syeda Anila Nusrat
Software Developer
Pakistan Pakistan
Name: Syeda Anila Nusrat

National University of Computer and Emerging Sciences
MS (Computer Science) 2010–2012
Federal Urdu University of Arts, Science and Technology
BS (Computer Science) 2004–2007

Professional Experience:-
Software Engineer at Systems Pvt Ltd (Nov 2010-Mar 2011)
Software Engineer at Syndustria Pvt Ltd (Jun2008-Feb2010)
Software Engineer(internee) at yEvolve Pvt Ltd (Feb2008-Apr 2008)

IDE: Ms Visual Studio 2005 and 2008
Programming Languages: C++.NET, C#.NET, VB.NET, ADO.NET
Web Technologies: ASP.NET, AJAX, Html, CSS, Java Scripting
Databases: SQL Server 2000, SQL Server 2005
Programming Methodologies: Multithreading and DLLs
Scheduling and Modeling tools: Ms-Project 2000, MS Visio, Rational Rose

Honors and Awards:-
Received Merit Certificate for scoring 3.81 CGPA on scale of 4.0 in BS(CS)

My professional Network

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Comments and Discussions

QuestionNot able to receive message Pin
Sagar Singh Biswakarma2-Dec-12 20:28
memberSagar Singh Biswakarma2-Dec-12 20:28 
QuestionLinkedin Profile GPRS Pin
AFFAN USMAN19-Nov-12 2:35
memberAFFAN USMAN19-Nov-12 2:35 
Questionusing huawei e1550 Pin
naq_ninetwo9218-Oct-12 12:09
membernaq_ninetwo9218-Oct-12 12:09 
Questionwhy not download? Pin
yf200917-Oct-12 21:40
memberyf200917-Oct-12 21:40 
GeneralMy vote of 5 Pin
Member 945602924-Sep-12 18:39
memberMember 945602924-Sep-12 18:39 
Questionhelp Pin
amin.naghdbishi21-Sep-12 6:33
memberamin.naghdbishi21-Sep-12 6:33 
QuestionRunning the application? Pin
Greyham13-Sep-12 12:10
memberGreyham13-Sep-12 12:10 
Generalmy vote of 5 Pin
shehbazshkh12-Sep-12 2:18
membershehbazshkh12-Sep-12 2:18 
very nice article...
BugError Pin
Puran Maury31-Aug-12 3:31
memberPuran Maury31-Aug-12 3:31 
GeneralRe: Error Pin
saqibsabir25-Dec-12 21:34
membersaqibsabir25-Dec-12 21:34 
GeneralMy vote of 5 Pin
Dirceu Albrecht28-Aug-12 16:12
memberDirceu Albrecht28-Aug-12 16:12 
QuestionAfter delete message, Read Message won't work properly Pin
wynnt3o12327-Aug-12 20:00
memberwynnt3o12327-Aug-12 20:00 
QuestionError: Response received is incomplete but still send SMS Message successfully??? Pin
bonfirebmt15-Aug-12 2:04
memberbonfirebmt15-Aug-12 2:04 
AnswerRe: Error: Response received is incomplete but still send SMS Message successfully??? Pin
fatihuyaroglu1-May-13 21:27
memberfatihuyaroglu1-May-13 21:27 
QuestionApplication Is not working Pin
Mohit_Patel9-Aug-12 3:59
memberMohit_Patel9-Aug-12 3:59 
Questionhi! Pin
roylandrix2-Aug-12 0:15
memberroylandrix2-Aug-12 0:15 
Questionhmmmm she is not a good developer Pin
Aziz BUkhari24-Jul-12 11:57
memberAziz BUkhari24-Jul-12 11:57 
QuestionHyperterminal substitute Pin
Anand scientist23-Jul-12 20:07
memberAnand scientist23-Jul-12 20:07 
AnswerRe: Hyperterminal substitute Pin
Greyham13-Sep-12 12:05
memberGreyham13-Sep-12 12:05 
QuestionCan't Send SMS Pin
SupraKing23-Jul-12 16:31
memberSupraKing23-Jul-12 16:31 
Questionunable to read sms Pin
aa007122345523-Jun-12 13:12
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GeneralMy vote of 3 Pin
Mr Pham1-Jun-12 22:20
memberMr Pham1-Jun-12 22:20 
GeneralRe: My vote of 3 Pin
waqas7867522-Dec-12 1:31
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QuestionNot able Reading SMS Pin
saleem muhammad30-May-12 23:40
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QuestionMessage reading error Pin
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