It's been a while since we'd seen any new SMS/GSM/serial remote interface projects. [Emanuele] sent in his version of a project to do just that. It uses a PIC16F84 and will send or receive commands. A pair of relays provide options for controlling whatever you want to hook it up to. You'll need a login, but he's released the full schematics and firmware. He developed this to find uses for old phones, but an alternative is to pick up a cheap calling card cell and dedicate it to a project like this. This seems like a great way to add an out of band alarm system to your house/car/robotic minion.
http://www.hackaday.com/2008/05/28/gsm-remote-control-project/