Most current Macintosh models come equipped with a line-in jack instead of a microphone jack. The consequence of this is that on  a standard analog 3.5mm headset the microphone will not work. If you do not have a microphone input jack, we strongly suggest you to purchase a USB headset or microphone. USB headsets and microphones act as seperate audio devices from your sound card. To configure your USB headset/microphone, simply access your system preferences, select the Sound control panel and adjust your microphone through the input tab and your headset (if you have one) through the output tab.