#include <Arduino.h>

String command = "";
void setup() {
  Serial.begin(9600);
  Serial.println("Type AT commands!");
}

void loop(){
  if (Serial.available()) {
    while(Serial.available()) { command += (char)Serial.read();delay(10); }
    Serial.println(command);
    command = ""; // No repeats
  }
  if (Serial.available()){ delay(20); Serial.write(Serial.read()); }
}