Voice Call Example

GSM Voice Call

This example shows you how to make a voice call using a GSM Shield, a device that allows you to control a SIM card. 
Using the GSM shield you can send/receive messages, get Internet connection and make voice calls. 
With this sketch you can call a remote phone after entering its number in the serial monitor. 
To hear the receiving voice and send yours, you'll need to connect headphones (or speaker) and a microphone.


  • Arduino board
  • Arduino + GSM Shield
  • Headphone and microphone
  • SIM card


/* Make Voice Call
This sketch, for the Arduino GSM shield, puts a voice call to
a remote phone number that you enter through the serial monitor.
To make it work, open the serial monitor, and when you see the
READY message, type a phone number. Make sure the serial monitor
is set to send a just newline when you press return.
* GSM shield
* Voice circuit.
created Mar 2012
by Javier Zorzano
This example is in the public domain.
// libraries
#include < GSM.h >
// PIN Number
#define PINNUMBER ""
// initialize the library instance
GSM gsmAccess; // include a 'true' parameter for debug enabled
GSMVoiceCall vcs;
String remoteNumber = ""; // the number you will call
char charbuffer[20];
void setup() {
// initialize serial communications and wait for port to open:
// connection state
boolean notConnected = true;
Serial.println("Make Voice Call");
// Start GSM shield
// If your SIM has PIN, pass it as a parameter of begin() in quotes
while (notConnected) {
if (gsmAccess.begin(PINNUMBER) == GSM_READY)
notConnected = false;
else {
Serial.println("Not connected");
Serial.println("GSM initialized.");
Serial.println("Enter phone number to call.");
void loop() {
// add any incoming characters to the String:
while (Serial.available() > 0) {
char inChar = Serial.read();
// if it's a newline, that means you should make the call:
if (inChar == '\n') {
// make sure the phone number is not too long:
if (remoteNumber.length() < 20) {
// let the user know you're calling:
Serial.print("Calling to : ");
// Call the remote number
remoteNumber.toCharArray(charbuffer, 20);
// Check if the receiving end has picked up the call
if (vcs.voiceCall(charbuffer)) {
Serial.println("Call Established. Enter line to end");
// Wait for some input from the line
while (Serial.read() != '\n' && (vcs.getvoiceCallStatus() == TALKING));
// And hang up
Serial.println("Call Finished");
remoteNumber = "";
Serial.println("Enter phone number to call.");
} else {
Serial.println("That's too long for a phone number. I'm forgetting it");
remoteNumber = "";
} else {
// add the latest character to the message to send:
if (inChar != '\r')
remoteNumber += inChar;