Connecting GSM/GPRS Shield + GPS Shield (SoftwareSerial/AltSoftSerial)

Hello everybody !

I'm trying to use the official Arduino GSM Shield (http://arduino.cc/en/Main/ArduinoGSMShield) with a Linksprite GPS shield(GPS Shield With SD Card Slot for Arduino V2.0 A - LinkSprite Playgound) + an Arduino UNO.

Code I used with the GPS shield :

void setup()
{
  GPS.begin(9600);
  Serial.begin(9600);
}
void loop()
{
  byte a;
    if (GPS.available() > 0 )
  {
    a = GPS.read(); // get the byte of data from the GPS
    Serial.write(a);
  }
}

Each shields works great separately but when not when they are all plugged. I've see the problem is that there are collision between the 2 because they use SoftwareSerial. It looks like the lib AltSoftSerial can resolve the problem but i don't understand how should I use it. I tried to replace the SoftwareSerial lib with AltSoftSerial but i changes nothing (nothing in the serial monitor window).

I've read this post that explain more : http://forums.adafruit.com/viewtopic.php?f=25&t=38764&sid=2758f15821f6f4cc5de1e88deb8ed481 but I'm bit lost... :frowning:

Have anyone an idea ?

PS : sorry for my bad english