Hi,
I think you are asking for the home automation project. By using 8051 and gsm you can control any appliances in your home by sending a sms from your mobile phone to gsm connected to controller so than you can switch on/off the appliances or you can get the status of the appliances from gsm to your mobile phone. As the appliances run on AC you can use the relay to control the appliance by use of small signal from controller.