Hi, my first showoff in here, so be lenient with it 
Maybe some other Arduino newbie like me finds this useful example. You may use at your own risk.
Brother of mine wanted to have a sms-controlled relay for turning his car heater (Webasto) on and off. Here is result, sms-controlled relay. Maybe there are better ways to do it, but this is how I've done it.
I've learn so far, that there are some issues regarding vibrations and shield connectors and I've a plan to make pcb where all the components are on same pcb. While waiting my inspiration, he (my brother) has to be satisfied with this solution.
I've done the code with AvrStudio 6.2 with Visual Micro, therefore in the zip file contains also some files for those softwares. There is a pdf-file as reference for the commands I've used to control device. Some commands are in Finnish but they are easy to change if needed.
Some pics will follow..
TommiP
Controller guide.pdf (226 KB)
GSM_relay_controller.zip (580 KB)
