sms.db and MMS messages: a question

[TheOtherMe]

Hello,

I'm trying to read MMS messages (it's a Cydia app! ).

I understood almost everything, except one thing.

I know MMS attachments are stored in
~/Library/SMS/Parts/
(with ~ = home folder = /var/mobile/ )

However, what I don't fully understand is how they are divided into subfolders.
For example:
~/Library/SMS/Parts/07/03/19-0.jpg
~/Library/SMS/Parts/(group id)/????/(message id)-(part id).jpg

"07" is the group (from sms.db's message_group; by the way, what happens when this is >99?), 19 is message's ID (ROWID in message table) and 0 is the part id.
But what does that "03" stand for?

Does anybody have any idea? I can't find any connection with any value in the sms.db file.

I thought it was the same as (message id), and before I restored my iPhone (restoring the backup after), it was.
But then it started again from 01!

Thanks in advance for your help.
Alessandro

//EDIT
Ok the "07", "03" etc are hex numbers (so after "09" comes "0a").
The doubt still remains, though: what comes after ff?