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

Hello everybody !

I'm trying to use the official Arduino GSM Shield ( 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()
void loop()
  byte a;
    if (GPS.available() > 0 )
    a =; // get the byte of data from the GPS

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 : but I'm bit lost... :frowning:

Have anyone an idea ?

PS : sorry for my bad english