Using Gammu with an old phone
This is not good.
Luckily, this is linux, so I was able to bash (ha!) something together on the command line. It's a combination of bash scripts and a C program that work together. I'm sure there's a better, more elegant way to do all this... but this works, and you're welcome to it.
The bash script to show new messages I'm especially happy with - not only does it display the unread messages, but you can reply to them right in your terminal window. Yay!
Please note that lines 116, 120, and 122 of the C code need edited for your appropriate pathnames before compiling. It should be ANSI C compatible with no unusual dependencies. The bash scripts need editing for pathnames as well.
You will also need to run
hcitool inqto get the bluetooth address of your phone.
I've got the code up at pastebin - here's the C program, the daemon is here (bash), and the script to show messages is here.
If you improve on them, do let me know!