I know the GSM shield doe not officially support the arduino due, but i'm wondering if there is any work around to make the DUE use the GSM shield to send and receive messages before i return it.
I don't have a Due...
Could you use a level shifter to talk to it through Serial1? You'll need a 5 volt supply to the shield, and whilst you might not be able to use the libraries all they are are a wrapper around Hayes AT commands.