Another alternative is to use the headphones that come with your mobile phone handset. You use these headphones to listen songs and also to answer voice calls. Connect this headphone to the headphone port of Mac mini and your headphone and microphone, both will work on mac.
Mac mini has only two ports – one for headphones and other for Line In. If we connect the generic headphone to Line In port, Mac does not detect it as a headphone. Hence lot of people have suggested online to use a battery powered headphone or a usb mic or a connection from preamp to use a mic.