Are there USB mobile broadband modems that don't require contracts?

I just got a 2009 Ford Fusion with Ford Sync (but not FordTouch). I would really like to make my car a mobile hotspot, and apparently all i need is a USB mobile broadband modem, but I have NO IDEA how that works… Do I need to get one through my phone provider (verizon)? I've seen that there are pre-paid modems, but i don't really understand how that would be any different than going through a provider. Are there any flat-rate options? Basically, is there any way to avoid a monthly fee? Thanks!

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