Hands free road talk on my laptop?

Hello. Recently a friend bought a new SUV with a speaker phone built in. My GPS is run by an XP Professional SP2 laptop on a car mount with USB ports built in. I’d like to have a hands free phone connection without the necessity of buying a cell phone, although I understand a microphone is necessary. Is there a way to use my laptop as a phone either with or without magic jack while driving cross country?