Your sketch works fine in my shield. Your problem may be caused by the condition that you introduced in gsmAccess.begin.
Change your gsmAccess.begin line to the following:
if((!PIN_OK) && gsmAccess.begin(PINNUMBER)==GSM_READY){
Your sketch works fine in my shield. Your problem may be caused by the condition that you introduced in gsmAccess.begin.
Change your gsmAccess.begin line to the following:
if((!PIN_OK) && gsmAccess.begin(PINNUMBER)==GSM_READY){