Please find the code attached to receive the IMEI number.

 

int8_t answer;
int x;

char SMS[200];

void setup(){

 
    Serial.begin(9600);  

   delay(3000);
    power_on();
    
delay(3000);
 Serial.println("Network...");
     while( (sendATcommand("AT+CREG?", "+CREG: 0,1", 500) ||
            sendATcommand("AT+CREG?", "+CREG: 0,5", 500)) == 0 );
            
delay(300);

    delay(3000);
    

    sendATcommand("AT+CMGF=1", "OK", 1000);    // sets the SMS mode to text
        Serial.println("IMEI number...");
       answer = sendATcommand("AT+CGSN", "", 2000);    // reads the first SMS
    if (answer == 1)
    {
        answer = 0;
        while(Serial.available() == 0);
        // this loop reads the data of the SMS
        do{
            // if there are data in the UART input buffer, reads it and checks for the asnwer
            if(Serial.available() > 0){    
                SMS[x] = Serial.read();
                x++;
                // check if the desired answer (OK) is in the response of the module
                if (strstr(SMS, "OK") != NULL)    
                {
                    answer = 1;
                }
            }
        }while(answer == 0);    // Waits for the asnwer with time out
        
        SMS[x] = '\0';
        
        Serial.print(SMS);    
        
    }
    delay(1000);
 

}


void loop(){
 
}

void power_on(){

    uint8_t answer=0;
    
    // checks if the module is started
    answer = sendATcommand("AT", "OK", 2000);
    if (answer == 0)
    {
        
    
        // waits for an answer from the module
        while(answer == 0){     // Send AT every two seconds and wait for the answer
            answer = sendATcommand("AT", "OK", 2000);    
        }
    }
    
}

int8_t sendATcommand(char* ATcommand, char* expected_answer, unsigned int timeout){

    uint8_t x=0,  answer=0;
    char response[100];
    unsigned long previous;

    memset(response, '\0', 100);    // Initialice the string

    delay(100);

    while( Serial.available() > 0) Serial.read();    // Clean the input buffer

    Serial.println(ATcommand);    // Send the AT command


        x = 0;
    previous = millis();

    // this loop waits for the answer
    do{
        // if there are data in the UART input buffer, reads it and checks for the asnwer
        if(Serial.available() != 0){    
            response[x] = Serial.read();
            x++;
            // check if the desired answer is in the response of the module
            if (strstr(response, expected_answer) != NULL)    
            {
                answer = 1;
            }
        }
        // Waits for the asnwer with time out
    }while((answer == 0) && ((millis() - previous) < timeout));    

    return answer;
}