I used to have an SIM800l module that I do not know exactly how I set up, but every time I deleted a SMS from the first memory location, the other SMS were moved up to the position of the first SMS, always occupying the position number one in storage.
Does anyone know how to set up my new module like that?
With such setup, in order to delete all SMS, I just repeatedly sent the command AT+CMGD=1 so that I didn't need to change the indices.
SMS messages changing position sound really strange, and I'm not sure it was what actually happened. Read all my answer to discover what I think could be the actual explanation.
TL;DR: you are lucky, because you can free your SMS memory with a single command: AT+CMGDA.
According to AT command guide its syntax is really simple:
AT+CMGDA=<type>
where <type> has a different meaning according to the +CMGF setting.
In text mode (after AT+CMGF=1):
"DEL READ" - Delete all read messages"DEL UNREAD" - Delete all unread messages"DEL SENT" - Delete all sent SMS"DEL UNSENT" - Delete all unsent SMS"DEL INBOX" - Delete all received SMS"DEL ALL" - Delete all SMSIn PDU mode (after AT+CMGF=0, that's not actually required, as it is the default value):
1 - Delete all read messages2 - Delete all unread messages3 - Delete all sent SMS4 - Delete all unsent SMS5 - Delete all received SMS6 - Delete all SMSWhat you need is to provide
AT+CMGDA="DEL ALL"
if you are operating in text mode, or
AT+CMGDA=6
if you are operating in PDU mode.
Even better, you can get rid of just read messages by issuing
AT+CMGDA="DEL READ"
if you are operating in text mode, or
AT+CMGDA=1
if you are operating in PDU mode. I suspect the latter was the command you actually used to provide.