This is a starter. I going to document what I have done here. I just need to get some time for it! Have a look at this while you are waiting ....
Also while waiting for me, have a look at http://www.gammu.org
For the sms daemon have a look at
I use smsd in mysql mode. It needs a own db and I am not really integrated that db into CiviCRM in any way. You could send sms just by inserting a row in Gammu smsd db outbox table. You could also specify when the sms is supposed to be sent.
In my first version of civicrm send sms via gammu I dont use sql to insert sms in SMSd outbox table. Instead i use the command.
It is perhaps a bad way and the lacy way to do it becouse it does the sql for me and putting the SMS in the outbox table and also if you have a multipart sms it creats that automatical.
I run CiviCRM on the same server as Gammu so I can do this system calls but if you have another server you could contact and send sms via mysql or any other way.
And also I think I could look up the right sql-queries in Gammu source code. And use them instead in CiviCRM. But then you need to connect to two DBs is there a neat way to do that?
I have done a simple diff to extract what I have done now when I am upgrading tp 2.06