I used the GSM library that comes together with arduino 1. Specifically the sendSMS part.
I managed sucesfully to send SMS.
Now the thing is, inside this library the SMS to send is stored in a char variable:
char txtMsg[200];
My question is, are you able to send the SMS, but store the message not in a char variable, but as a String?
I would test it myself but now i only have one SIM card, and for some reason my network is blocking it (that is another thread to be started btw)