gsm at commands sim900

hello
i wand to read sms from sim 900 on text mode!

with the AT+CMGL="REC UNREAD"
i get a list from all unread sms in the phone
but i wand to read only one at the time!

so how to get on the total number of unread sms , and the index number of the sms so to choose to read only spesific sms

thanks