analog reference

Using Arduino Microcontrollers
8 
val1 = digitalRead(inputPin1); // read input value from PIR
    if (val1 == HIGH) { // check if the input is HIGH
      mySerial.print("ATD +919*********;");//dial the number

I should point out that loop is executed thousands of times a second, so you are going to be dialing that number an awful lot.