FS stopped receiving SMS messages.  I suspected the SIM is filled up.  By using AT commands, indeed there are in the SIM. 

Question 1: Does mod_sms automatically delete read messages?
Question 2: Does mod_sms read UNREAD messages from the SIM during start-up?
Question 3: Do I need to flush out these messages before so it will work again?

Thanks.
/Nandy