Use Earphone Or Headphone As Microphone [tips]
The laptop my office gave me doesn't have an internal microphone. I only realized it when I had to make a voice call. I have couple of earphones. I used one of it as microphone by simply plugging it in the microphone jack and using the ear piece as mic. Any earphone or microphone will work. You don't need earphone that comes with mobile phones that has mic in it.