The thing you plug into the side of the laptop is technically just a minuature cell phone radio with a USB connection. Its not different than your phone from a technology standpoint.
Depending on your speed requirements and usage I would look at:
Verizon
Millenicom
Internet to Go (Through Walmart)
Purchase a MIFI Mobile hotspot and a corresponding plan based on your needs.
You may want to do some searching here on the forum or read through these articles for a better understanding:
Changing Gears-Internet AccessRV Internet and Mobile WIFI * The On the Go GuideYour RV Lifestyle - RV Internet Access