Problems with AT commands SKU:TEL0051 and Arduino UNO

AT
AT+CREG?
21326
ÿ©
Ä
HRmDdYd
0
0
"

+TCHFTUANT:O =1

[

AT+SAPBR=3,1,"APN","internet"
AT+SAPBR=3,1,"Contype","GPRS"
AT+SAPBR=1,1
AT+HTTPINIT
AT+HTTPPARA="CID",1

void setup()
{
  Serial.begin(9600); 
   pinMode(3,OUTPUT);
    pinMode(4,OUTPUT);
    pinMode(5,OUTPUT);
    digitalWrite(5,HIGH);
    delay(1500);
    digitalWrite(5,LOW);
    digitalWrite(3,LOW);//enable GSM TX?RX
    digitalWrite(4,HIGH);//disable GPS TX?RX
    delay(2000);
    //delay(20000);        
    start_GSM();    
    delay(5000);     
}
char* serialGetString()
{
  int maximo = 500;
  char cadena[500];
  unsigned i=0;
  char sIn;
  --maximo;        
  while (Serial.available() && i<maximo)
    {
      sIn=Serial.read();
      cadena[i++]=sIn;
      delayMicroseconds(500);
      i++;
    }
  cadena[i++]='\0';
  return cadena;
}
void loop () 
{    
}

void start_GSM(){    
    Serial.println("AT");    
    delay(2000);
    Serial.println("AT+CREG?");
    delay(2000);     
    Serial.println('AT+GSN'); //this line returns the value 21326 me directly on the screen when I run the AT + GSN command but not the IMEI
    delay(2000);   
    Serial.println(serialGetString());
    Serial.println("AT+SAPBR=3,1,\"APN\",\"internet\"");
    delay(2000);
    Serial.println("AT+SAPBR=3,1,\"Contype\",\"GPRS\"");
    delay(2000);
    Serial.println("AT+SAPBR=1,1");
    delay(10000);
    Serial.println("AT+HTTPINIT");
    delay(2000);
    Serial.println("AT+HTTPPARA=\"CID\",1");
    delay(2000);
 }

Serial.println(Serial.read());