SMS related messages are all sent over SAPI=3. But in addition
to that, we also need to send it over the correct link identifier,
i.e. SACCH or main signalling channel
we now have the full path from the MS into the database (SUBMIT), as well as
back from the database to the MS (DELIVER). The database gets correctly
updated once a SMS has been successfully delivered.
What's still missing is the periodic scan over all undelivered messages,
trying to deliver them to the respective MS. So far, you have to manually
trigger this on the telnet interface with 'sms send pending 1'