Read data from SIM using AT Commands.

Hi,

i have a sms system. it is used to receive messages and store it. it works fine. but when the system is not loaded and new sms arrives. it normally gets stored in SIM. but when i again open the system., it is not receiving the messages stored in the SIM.

so now i want to know the at commands using which i can read the messages in the SIM and whether i can read only the unread messages from the SIM.