Hi,
I'm new and I understand there is nothing here you can ask that way, but... it's a strange you get a library released which won't even compile.
I did replace <return NULL;> with <return "";> in a couple of GSM library files (i.e. GSM3ShieldV1ScanNetworks.cpp & GSM3ShieldV1ModemVerification.cpp).
Now it compiles... hope it works as well? 
Cabbi