well, one way of doing it, assuming you use tone phones where you are, is to plug the output of the phone (the speaker) into the mic socket of your computer.
Then write some code to check the frequency of the noise comign in from the phone. When it 'hears' a certain frequency, then the person is pressing a certain button.
Then write some code to check the frequency of the noise comign in from the phone. When it 'hears' a certain frequency, then the person is pressing a certain button.