Index of last sms received

Hi ,

I'm trying to use the sim800l module to display the most recent message when received. I know that the AT+CMGR command needs the index of the message in order to read it. The problem is that I don't know the way the messages are indexed; is index 1 referring to the last one stored or the first one ever stored ? I also don't know if it's the Sim card storage or the module's storage (if that
actually exists) that is used.