I'm currentliy working with the GSM-Shield, and it connects sometimes, but isn't reliable, sometimes it doesn't get past the GSM.begin() and shows things like:
120 23>AT+CGREG?%13%%13%%10%+CGREG: 0,2%13%%10%%13%%10%OK%13%%10%
23 54>AT+CGREG?%13%%13%%10%+CGREG: 0,2%13%%10%%13%%10%OK%13%%10%
I really don't what the reason could be, the GSM shield is working, because sometimes it connects and sends an SMS just like it should, no matter whether there's an external power source.
According to another post (http://forum.arduino.cc/index.php?topic=243407.0
), the CGREG has the following meaning:
This could mean, that the operator network may have some issues, my other guess is, that's a problem in the library, but then again it wouldn't work at all.