Attached is a text file for an SMS controller project that I did a few years ago, using a MELabs LabX-USB demo board connected to a Multi-Tech SMS modem using CDMA (Verizon Wireless.) The program utilizes a serial interrupt handler that I came across, you could easily rewrite this to use Darrel's instant interrupts. Melanie had posted an example on serial communications that I modified to read the SMS message and determine if a) the command is valid, and b) the password is valid. Bruce and Darrel have both provided temperature sensor examples, which I used to read a Dallas 18s20 sensor.
To use the program you send a text message to the unit that consists of a command, such as Light, and a password, 1234. If the unit receives a valid command and password, it goes to a subroutine, Light: in this example, and turns on my foyer table lamp. It then sends a text message back to the number that sent the original message, saying that it has turned on the lamp.
Al, (Aratti) has suggested that spam might be a problem if you send a response back to anyone who sends a message, but Verizon Wireless fights spam really well, I've only gotten two spam text messages ever, but as they say, your mileage may vary.