No. Magic Jack requires a USB port. While you can connect USB devices to the iPad using the Camera Connection Kit, only a few standard devices are supported. Magic Jack is not.
However; there are a number of apps for the iPad that can be used to make phone and video calls to others. Some are free, some cost a bit. Apps that work with Google Voice are probably worth looking into. Whistle Phone also looks interesting. I've heard good things about both.
I haven't used/tried any of these, since I barely make a dent in my iPhone's plan.