I have developed a system like this for the automotive industry that controls vehicles through the GSM SMS. It also send an SMS to a specified phone if the vehicle battery fall below an acceptable level. to bring the voltage to the required for the Arduino I use a buck converter that will allow for a voltage as high as 24 and as low as 6 volts to driver the system. This can be built with a GSM shield sat on an Arduino Uno and some simple relay shields.
Have a look at my website www.EmbeddedAT.com
and decide if you think i have what you need to do this job for you.