Eseguire HTTPGET dopo aver ricevuto una chiamata

Il mio obiettivo è di far eseguire una get dopo aver ricevuto una chiamata telefonica.
Ho preso come spunto lo sketch seguente che funziona correttamente:

#include "SIM900.h"
#include <SoftwareSerial.h>
//We don't need the http functions. So we can disable the next line.
//#include "inetGSM.h"
#include "sms.h"
#include "call.h"

//To change pins for Software Serial, use the two lines in GSM.cpp.

//GSM Shield for Arduino
//www.open-electronics.org
//this code is based on the example of Arduino Labs.

//Simple sketch to check if an incoming call is from an authorized
//number and in this case, send to this number an SMS with the value
//of a digital input.

//We have to create the classes for SMSs and calls.
CallGSM call;
SMSGSM sms;

char number[20];
byte stat=0;
int value=0;
int pin=1;
char value_str[5];

void setup() 
{
  pinMode(pin,INPUT);
  //Serial connection.
  Serial.begin(9600);
  Serial.println("GSM Shield testing.");
  //Start configuration of shield with baudrate.
  //For http uses is raccomanded to use 4800 or slower.
  if (gsm.begin(2400))
    Serial.println("\nstatus=READY");
  else Serial.println("\nstatus=IDLE");
};

void loop() 
{
  //Chekcs status of call
  stat=call.CallStatusWithAuth(number,0,0);
  //If the incoming call is from an authorized number
   if(stat==CALL_INCOM_VOICE_AUTH){
    //Hang up the call.
    call.HangUp();
    delay(2000);
    //Check the value of the input.
    value=digitalRead(1);
    //Convert the int to a string.
    itoa(value,value_str,10);
    //Send an SMS to the previous number with
    //the value read previously.
    sms.SendSMS(number,value_str);
  }
  delay(1000);
};

Ho modificato il codice in modo che invece di inviare un sms esegua la get

#include "SIM900.h"
#include <SoftwareSerial.h>
#include "inetGSM.h"
//#include "sms.h"
#include "call.h"

//To change pins for Software Serial, use the two lines in GSM.cpp.

//GSM Shield for Arduino
//www.open-electronics.org
//this code is based on the example of Arduino Labs.

//Simple sketch to start a connection as client.

InetGSM inet;
CallGSM call;
//SMSGSM sms;

char msg[50];
int numdata;
char inSerial[50];
int i=0;
boolean started=true;
int pin=1;
byte stat=0;
char number[20];


void setup() 
{
  pinMode(pin,INPUT);
  //Serial connection.
  Serial.begin(9600);
  Serial.println("GSM Shield testing.");
  //Start configuration of shield with baudrate.
  //For http uses is raccomanded to use 4800 or slower.
  if (gsm.begin(4800)){
    Serial.println("\nstatus=READY");

  }
  else Serial.println("\nstatus=IDLE");
  
};

void loop() 
{

 stat=call.CallStatusWithAuth(number,0,0);
 //If the incoming call is from an authorized number
  //saved on SIM in the positions range from 1 to 3.
  if(stat==CALL_INCOM_VOICE_AUTH){
  //Hang up the call.
    call.HangUp();
    delay(2000);
    started=true;
              if(started){
                started=false;
//                //GPRS attach, put in order APN, username and password.
//                //If no needed auth let them blank.
               if (inet.attachGPRS("wap.tim.it", "", ""))
                  Serial.println("status=ATTACHED");
                else Serial.println("status=ERROR");
                delay(1000);
//                
//                //Read IP address.
                gsm.SimpleWriteln("AT+CIFSR");
                delay(5000);
//                //Read until serial buffer is empty.
                gsm.WhileSimpleRead();
//              
//                //TCP Client GET, send a GET request to the server and
//                //save the reply.
              numdata=inet.httpGET("www.google.com", 80, "/", msg, 50);
//                //Print the results.
                Serial.println("\nNumber of data received:");
                Serial.println(numdata);  
             
                Serial.println(msg); 
          
              }
  }
  delay(1000);
};

Purtroppo sul monitor seriale mi appaiono una serie di gggggg .
Se provo a commentare la parte che si occupa di ricevere la chiamata, la get viene eseguita, viceversa se commento la parte relativa alla
inet.attachGPRS e quindi della get , il codice che si occupa di attendere le chiamate viene eseguito.
Non riesco a trovare un modo per far convivere e funzionare le due attività insieme, come avviene invece per lo sketch attesa chiamate e invio sms.

Spero in un vostro aiuto