Magicjack presents itself as a telephone jack. So, plug it into your router, then plug it into a speakerphone and away you go.
Whatever options would exist for having a home computer dial your landline telephone are the same options that would be available.
I doubt it will work very well, though. VOIP is prone to dropping calls and in a moving automotive environment on a 3G router, would be a particular challenge. Also, of course, the cost of the 3G router, but that might be okay if you wanted internet in the car, anyhow.