saving and indexing messages on SIM900

I use a MEGA and a GPRS SIM900 shield to communicate with a smartphone by SMS
I'd like to save some parameters and warnings messages on the shield,
the SIM900 shield also had a battery, in the ways I can keep and use the time, instead of buy RTC shield
On the same idea, why not use the free memory on the SIM900 shield ?
I wish save it on the "ME" part and not the "SM" part (sim card), because size of ME is greater than the SIM card and also the SIM can change if its one other users (but messages remains the same).

I use the command AT + CPMS, then AT + CMGW,
At the moment I can only save one message this way
But I want save several messages without phone number
So I want save and index messages only
I want to give an index to read it

How to do ?

Thank's for advice and help.

Post your code

Hello RudiAhlers,
I'll post the code as it is now, dirty with a lot of mistakes, but functional
I can send more than fifty order ON/OFF through a SMS to a ARDUINO MEGA,

I use the alphabet (uppercase and lowercase) to make a difference, and 1 or 0 for on / off,
26 uppercase + 26 lowercase means almost all my input/output on the Arduino MEGA

I always start with # #
the sms is : # # A1B1 switch ON pin 5 and 6 and so on

This is just for fun and learning .

send_GSM1.ino (27.8 KB)