Use two or more Arduino GSM sheilds with Arduino mega (or uno)

Is there any chance of create a successful multi network message delivery system with two or more GSM shields attached to one arduino.

What we are going to do…

First user input a telephone no…
Then arduino checks it’s prefix (In sri lanka we use different prefix for different networks) Like 077-xxxxxxx / 072-xxxxxxx
He selects the matching GSM sheild that includes matching network sim
Then send the SMS via that GSM module.

We are going to build a low cost sms system as one of our projects for school. Is there any way of success using more than one arduino gsm shield with arduino uno or mega. We only have one GSM shield at time. Before buying another one (of cource… we are just school students. So we can’t afford cost) we are asking about this.

Thanks in advance (Sorry about my bad english, I'm not a native. :) )

with two or more GSM shields attached to one arduino.

Two or more of which GSM shield? Typically, the Arduino and GSM communicate using SPI. As long as each shield has a different CS (chip select) pin, you can communicate with any number of SPI devices at a time. Of course, you won't be able to just stack them up, because, as shields, the CS pin is hard-wired.

PaulS:
Typically, the Arduino and GSM communicate using SPI.

Really? The ones I've used -- a SM5100 based job from Sparkfun and a SIM900 based one from Itea both just use vanilla async serial. The official Arduino GSM shield uses async serial on pins 2 and 3 -- and uses Software Serial to drive it.

I believe that running two or more GSM modules -- I hesitate to say shields because the shield connections are too inflexible -- should be possible, but you would likely want to use a MEGA that has more hardware UARTs. It is not so practical to run multiple Software Serial instances concurrently, and for for this type of application you'd kind of need to talk to either or both modules at any time.

Really?

No. I was thinking Ethernet shield, while my eyes were seeing GSM shield, and my fingers were busy tapping away.

You are correct. The communication between GSM and Arduino is typically serial.