Depending on your level of risk taking, you may be interested in something like this from eBay: http://www.ebay.com/itm/MOBILE-HOTSPOT-FLASHED-TO-VERIZON-PP...
The units are flashed and use Verizon's prepaid Internet plans but are effectively unlimited - if you prepay your account for a year - you get unlimited 3G data during that time for about $100/yr.
I couldn't quite believe when I stumbled across it - but it reminds me of hacked satellite encryption back in the day. Hard to believe this would actually work - or keep working for a long time - but based on some questioning - these eBay vendors stand behind their products....
Perhaps someone has a better idea of how these actually function....I don't.