Lowering delay when sending multiple SMS I would like to use Arduino for bulk SMS sending. Right now, when I'm sending an SMS with 160 characters, I have to delay the sending of the next one for 9500 milliseconds. If I don't do that, some of the messages do not get sent. Is it possible to somehow lower that delay (by changing my code, using a different Arduino or SIM model, etc)?  I am using Arduino Uno and SIM800L (external power supply). This is my code.

#include &lt;SoftwareSerial.h&gt;


#define SIM800_TX_PIN 11
#define SIM800_RX_PIN 10

//Create software serial object to communicate with SIM800
SoftwareSerial serialSIM800(SIM800_TX_PIN,SIM800_RX_PIN);

void setup() {
  int a;
  String b =  "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nam eu eleifend nunc. Suspendisse eget eros metus. Nunc ut nunc vel enim placerat egestas. Sed molestie, sapien sit amet bibendum --";
  String d = "";
  int textLen;

  Serial.begin(9600);
  while(!Serial);

  serialSIM800.begin(9600);

  for (a =1; a &lt; 5; a++) {
    textLen = b.length()+2;
    char c[textLen];
    d = "";
    d = b + a;
    d.toCharArray(c,textLen);
    serialSIM800.write("AT+CMGF=1\r\n");
    delay(200);

    serialSIM800.write("AT+CMGS=\"+381*******\"\r\n");
    delay(200);
    //Send SMS content
    serialSIM800.write(c);
    delay(200);

    //Send Ctrl+Z / ESC to denote SMS message is complete
    serialSIM800.write((char)26);
    delay(9500);

    Serial.println("SMS Sent!");
  }
}

void loop() {
}
It because a single SMS has 160 character limit. If you send more than 160 characters, those are transmitted by a process called concatenation(just googled out).
You can send at a faster rate by avoiding this process and sending 2 different messages which are of length less than 160. Hope it satisfies your query.