Verizon Wireless has prepaid aircards so you just put in airtime when you're going to use it.

You get a lot more data with a monthly account though so look into both options.

If you have a cell phone with them, many of them allow you to add tethering through your phone so you can connect to the rev A 3G network through your phone and just add the tethering feature when you're going to travel.

Visit www.verizonwireless.com for more details specific to your area.