how to write a C# program for parallel port to control a relay based circuit?

actually i know the AT commands for modem like how to dial a number or receive a call. but didnt work with C# before. so i want a sample code for this project.

Systemoverview
User from anywhere being GSM available can make a call to system to check the status of appliances or control them . System in return checks the authenticity of the number and if it is from the preconfigured number then it follows the instruction otherwise it discard the call. As computer receives a call timer starts and it automatically discard the call after few seconds. The voice is understood by the Microsoft speech reorganization engine that is installed in the system. If the command is about changing the status of appliances it passes the signal to parallel port to follow the instruction like turn the appliances on or off. This can be done through relay based circuit. If command is to check the status of appliances the system returns the voice message to preconfigured number using AT Commands telling the status of appliances. On the other hand if system finds any kind of intrusion like opening of entrance door etc in the home it sends the voice message to user telling him about the intrusion as

Algorithm is
Begin
If hardware test fails
Return
End
Else if hardware tests succeed then
Successful communication
If system gets a call
Check the authenticity
If call not from the preconfigured number
Aboad the call
Else
Receive the call and listen the command
If command is about controlling the appliances
Send the signal to parallel port and control them
sends the respective voice message
If command is about knowing the status of appliances
Check the parallel port status of appliances and sends the status to that number
If system sense some intrusion in the home
Return the voice message to preconfigured number
End