I've been waffling for a long time on whether or not to get an EVDO card for my laptop. On the one hand, I rarely travel, and I usually have a WiFi or LAN connection available. On the other hand, when I do travel (several times a year), I'm invariably aggravated by the difficulties I have in getting a decent connection.
I've looked into temporary rentals of EVDO cards and services, but for some reason, the carriers have decided that they can make more money by forcing consumers to commit to long term contracts. The few people who do rent EVDO have outrageous prices like $75/week.
I just discovered, however, that I can use my T-Mobile smartphone as a USB modem for my laptop. Their EDGE service, which provides connection speeds of 144K, costs $29.95 per month, doesn't require any special equipment, and can be activated or deactivated at any time. I can use it for a week, and only pay a pro-rated amount.
I haven't tried it out yet, but if you're looking for a short-term wireless access solution, you might want to check it out.