I got a message where a forum user asked for a code about this. I don't know whether he got what he wanted, but here is a crude project to handle an old ITEAD GSM modem. AT commands are standardized but I have used the code only with the Itead PC board using Sim.com's Sim 5216e module. I had to solder some wires myself to get the thing working, and lower the baud rate to 38kBd (with AT commands).
The code is too long for a post, but I made zip file of it.
Names and comments are Finnish.
I hope this helps.
vastaava5_08042015_to_forum.zip (4.58 KB)