WE use an AT&T 3G air card (free at Costco with two year sign up at $60/month with 5GB per month usage, way more than enough) which plugs into any USB port on any computer. If we want to get on line with more than one computer, we plug the air card into our NetGear 3G Broadband Wireless Router MBR624GU ($119.95 at Frys) which runs on 12V
and comes with a 110v adaptor. That way friends we are camped with can, when given the code, get on line as well.
We also use this setup at our home in Walnut Grove, CA, which is way out in the country. There, we have to use an outside antenna with an amplifier to enhance the cell service. The only other broadband in Walnut Grove is the local phone company, also $60 per month, and no good on the road.
Works well for us.
Looks like the MiFi would do much the same thing.